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ROOT  BEHAVIOR  AND  CROP  YIELD  UNDER 

IRRIGATION 


By  Frank  C.  Jean  and  John  E.  Weaver 


» 


LlDhfu:!  in 


OCT  8  1924 


UNIVERSITY  Of  ILLINOIS 


Published  by  the  Carnegie  Institution  of  Washington 
Washington,  September,  1924 


CARNEGIE  INSTITUTION  OF  WASHINGTON 

Publication  No.  357 


Copies  of  tfcis  M 
first  issued 
SEP  12  1924 


JUDD  &  DETWEILER,  INC. 
WASHINGTON,  D.  C. 


-Vz  °-nbV 


6  3  *2. 

1  VW 


CONTENTS. 


List  of  illustrations . 

Introduction . 

Location  and  description  of  stations 

Crops  and  methods . 

Environmental  conditions,  1922 .... 

Experiments  with  alfalfa . 

Experiments  with  wheat . 

Experiments  with  sugar  beets . 

Experiments  with  potatoes . 

Experiments  with  corn . 

Environmental  conditions,  1923 .... 

Experiments  with  alfalfa . . 

Experiments  with  wheat . 

Experiments  with  sugar  beets . 

Experiments  with  potatoes . 

Experiments  with  corn . 

Summary  and  conclusions . 

Bibliography . 


Page 

iv 

3 

6 

9 

12 

15 

21 

26 

33 

36 

44 

48 

49 
52 
55 
57 
60 
66 


HI 


vJS 


7704 


LIST  OF  ILLUSTRATIONS. 


PLATES. 

Plate  1. 

A.  Yield  of  alfalfa  from  one  square  rod  of  dry  land  (left)  and  irrigated  land  (right) 

on  July  26,  of  first  season’s  growth. 

B.  Yield  of  grain  from  one  square  rod  of  lightly  irrigated  wheat  (two  containers  on 

left),  fully  irrigated  but  more  sandy  soil  (center),  and  dry  land  (right),  1922. 

Plate  2. 

Wheat,  1922:  (A),  dry  land;  (B),  lightly  irrigated. 

Plate  3. 

Sugar  beets,  July  8,  1922:  (A),  dry  land;  (B),  fully  irrigated. 

Plate  4. 

Potatoes,  July  7,  1922:  (A),  dry  land;  (B)  lightly  irrigated;  (C),  fully  irrigated. 

Plate  5. 

Corn,  July  10,  1922:  (A),  dry  land;  (B),  lightly  irrigated. 

Plate  6. 

A.  Marquis  spring  wheat  grown  on  fully  irrigated  soil  (left),  lightly  irrigated  but  less 

sandy  soil  (center),  and  dry  land  (right),  1922. 

B.  Wheat  (3  feet  high)  grown  on  dry  land,  1923,  and  photographed  to  the  same  scale. 

TEXT  FIGURES. 

1.  Hygrothermograph  record  for  third  week  in  July,  1923,  showing  usual  wide  fluctuations 

between  day  and  night  temperature  (light  line)  and  humidity  (heavy  line). 

2.  Average  day  temperature  (heavy  lines)  and  average  night  temperature  (light  lines) 

in  dry-land  (solid  lines)  and  irrigated  plats  (broken  lines),  1923. 

3.  Average  daily  evaporation  in  dry-land  (solid  line)  and  irrigated  plats  (broken  line),  1922. 

4.  Soil  temperature  in  dry-land  (solid  lines)  and  irrigated  plats  (broken  lines),  at  depths  of 

3  inches  (light  upper  lines),  6  inches  (heavy  lines),  and  12  inches  (light  lower 
lines),  1922. 

5.  (A)  and  (B),  roots  of  alfalfa  plants  2  months  old,  those  in  dry  land  with  greater  depth 

and  longer  branches;  (C)  and  (D),  plants  3  months  old,  the  one  from  the  dry  land 
having  the  greater  number  of  branches. 

6.  Alfalfa  near  the  end  of  the  first  season’s  growth:  (A),  dry  land;  (B),  irrigated  soil. 

7.  Root  system  of  alfalfa  on  July  2  of  second  year  of  growth:  (A),  dry  land;  (B),  irrigated 

soil. 

8.  Roots  of  wheat:  (A)  and  (B),  6  weeks  old,  the  former  in  soil  where  little  water  occurred 

in  the  second  foot:  (C),  (D),  and  (E),  2.5  months  old  in  dry  land,  lightly  irrigated 
(more  clayey)  and  fully  irrigated  (sandier)  soils  respectively. 

9.  Roots  of  wheat  at  maturity:  (A),  dry  land;  (B),  lightly  irrigated;  and  (C),  fully  irrigated 

soil,  1922;  (D),  dry  land,  1923. 

10.  Sugar  beets  about  2  months  old:  (A),  dry  land  (practically  no  chresard  in  second  foot); 

(B),  irrigated  soil,  1922. 

11.  Sugar  beets  about  3  months  old:  (A),  dry  land  with  low  holard  of  subsoil;  (B),  fully 

irrigated  soil,  1922. 

12.  Sugar  beets  on  September  12:  (A),  dry  land;  (B),  fully  irrigated  soil,  1922. 

13.  Sugar  beet  roots  about  2  months  old:  (A),  dry  land;  (B),  irrigated  soil;  1923. 

14.  Sugar  beets  about  3  months  old:  (A),  dry  land;  (B),  irrigated  soil;  1923. 

15.  One-half  of  the  root  system  of  potatoes  when  6  weeks  old:  (A),  dry  land;  (B),  irrigated 

soil.  And  about  9  weeks  old;  (C),  lightly  watered,  and  (D),  fully  irrigated  soil, 
1922;  (E),  mature  plants,  dry  land,  1923. 

16.  Root  system  of  6-weeks-old  corn:  (A),  dry  land;  (B),  lightly  irrigated;  (C),  fully  irri¬ 

gated  soil. 


IV 


List  of  Illustrations 


v 


17.  Corn  about  8  weeks  old:  (A),  dry  land;  (B),  lightly  irrigated;  (C),  fully  irrigated  soil. 

18.  Dry-land  corn  on  September  12. 

19.  Corn  in  fully  irrigated  soil,  September  13. 

20.  Corn  in  lightly  irrigated  soil,  September  13. 

21.  Average  day  air-temperatures  (upper  lines)  and  average  night  air-temperatures  (lower 

lines)  in  dry-land  (solid  lines)  and  irrigated  plats  (broken  lines),  1923. 

22.  Average  day  humidity  (lower  lines)  and  average  night  humidity  (upper  lines)  in  the 

dry-land  plat  (solid  lines)  and  in  the  irrigated  plats  (broken  lines),  1923. 

23.  Average  daily  evaporation  in  dry-land  (solid  line)  and  irrigated  plats  (broken  line),  1923. 

24.  Soil  temperature  in  dry-land  (solid  lines)  and  irrigated  plats  (broken  lines)  at  depths  of 

3  inches  (light  upper  lines),  6  inches  (heavy  lines),  and  12  inches  (lower  light  lines), 


ROOT  BEHAVIOR  AND  CROP  YIELD  UNDER 

IRRIGATION 


BY 

Frank  C.  Jean, 

Professor  of  Biology,  Colorado  State  Teachers ’  College, 

AND 

r 

John  E.  Weaver, 

Professor  of  Plant  Ecology  in  the  University  of  Nebraska. 


1 


ROOT  BEHAVIOR  AND  CROP  YIELD  UNDER  IRRIGATION. 


INTRODUCTION. 

More  than  half  of  the  surface  of  the  earth  receives  insufficient  precipita¬ 
tion  for  the  most  favorable  growth  of  crops.  The  best  method  of  making 
up  this  deficiency  is  through  the  application  of  water  by  irrigation.  Hence 
the  economical  use  of  irrigation  water  is  one  of  the  chief  problems  of  agri¬ 
culture  in  arid  regions.  Since  much  more  land  is  available  than  can  be 
irrigated  by  the  supply  of  water,  even  when  methods  of  greatest  economy 
are  employed,  the  welfare  of  these  regions  demands  that  the  irrigation 
water  be  used  as  efficiently  as  possible  (cf.  Harris,  1916).  It  has  been 
estimated  that  in  the  United  States,  when  all  possible  economies  have  been 
put  into  operation,  the  irrigated  regions  can  be  enlarged  to  about  four  times 
the  present  area  (Harris,  1920).  The  magnitude  of  crop  production  under 
irrigation  may  be  recognized  from  the  fact  that  Colorado  alone,  which 
maintains  a  ranking  in  irrigation  development  second  to  that  of  California, 
has  an  irrigated  area  of  over  3,000,000  acres,  yielding  an  annual  revenue  at 
current  prices  of  over  $100,000,000  (Hemphill,  1922). 

Considerable  experimental  work  has  been  done  to  determine  the  proper 
use  of  irrigation  water,  but  notwithstanding  the  direct  relation  of  roots 
in  furnishing  the  plant  with  water  and  nutrients,  the  results  have  been 
measured  only  in  crop  yield  and  little  attention  has  been  given  to  the 
fundamental  relation  of  roots  to  water  and  air.  In  this  lies  the  proper 
understanding  of  the  problem. 

Root  systems  of  crop  plants  are  usually  if  not  always  very  responsive 
to  environmental  change.  They  respond  to  differences  in  water-content 
and  aeration,  both  in  amount  and  direction  of  growth,  and  by  varying 
these  factors  by  the  application  of  more  or  less  water,  not  only  the  develop¬ 
ment  of  the  root  system  but  also  the  above-ground  plant  parts  and  yield 
can  be  varied,  since  a  close  correlation  exists  between  the  growth  of  roots 
and  tops.  The  application  of  an  excess  of  water  results  not  only  in  the 
waste  of  the  water,  loss  of  labor  in  applying  it,  and  injury  to  the  soil,  but 
often  also  in  delayed  germination  and  delay  in  time  of  maturity  with  its 
attending  greater  liability  to  rust  and  attack  by  other  diseases,  as  well 
as  decrease  both  in  quantity  and  quality  of  yield.  Time  of  application  is 
of  scarcely  less  importance.  As  regards  saving  of  water,  Howard  (1918) 
points  out  that  while  irrigated  wheat  in  the  dry,  windy  Quetta  Valley  in 
Baluchistan  is  often  watered  six  times,  a  method  of  growing  the  crop  on 
a  single  irrigation  has  been  worked  out  under  which  the  yields  are  often 
higher  and  the  harvest  about  a  month  earlier.  He  further  states  that  at 
least  a  third  of  the  water  used  on  the  wheat  crop  in  the  Punjab  district 
of  India  is  wasted  (cf.  Clements,  1921).  Widstoe  (1914)  was  probably 
the  first  to  show  that  there  is  a  steady  decrease  in  the  yield  of  wheat  per 

3 


4 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


acre-inch  of  water  as  the  irrigation  of  a  field  is  increased,  and  that  exces¬ 
sive  irrigation  may  produce  an  actual  decrease  in  total  yield.  Experiments 
have  further  shown  that  when  water  is  applied  at  the  proper  time  two  or 
three  irrigations  give  as  good  results  as  the  use  of  more  water  (Harris, 
1917).  Since  crops  differ  greatly  in  the  amount  of  water  which  they  can 
profitably  use  (Knapp,  1922),  as  well  as  in  their  response  to  adverse  aerial 
environment,  a  thorough  study  of  the  root  systems  is  not  only  warranted 
but  imperative  for  an  adequate  explanation  of  their  behavior. 

Germination  is  more  rapid  and  complete  in  a  soil  containing  a  moderate 
amount  of  water,  as  has  been  pointed  out  by  Harris  (1918)  and  others. 
The  formation  of  a  surface  crust  as  a  result  of  irrigation  not  only  forms 
a  mechanical  barrier  to  the  tender  seedling,  but  may  likewise  profoundly 
affect  aeration.  For  example,  in  Northern  India,  following  irrigation,  a 
crust  bakes  on  the  soil,  and  this  is  quite  impermeable  to  air,  as  may  be 
shown  by  immersing  a  portion  of  the  hardened  surface  in  water,  when  the 
air  escapes  sideways  and  not  through  the  surface  skin  (Howard,  1918). 

The  time  of  ripening  is  delayed  by  overirrigation,  as  has  been  repeatedly 
shown  for  many  crops.  Indeed,  it  has  been  found  that  soil  moisture  was 
capable  of  influencing  the  ripening  period  to  such  an  extent  that  varietal 
characteristics  were  lost  (Seelhorst,  1911).  Balls  (1919),  working  with 
the  cotton  plant  in  Egypt,  has  shown  that  not  only  was  maturity  delayed 
by  an  excess  of  irrigation  water,  but  also  that  when  the  water-table  was 
again  lowered,  a  new  growth  of  tops  took  place  synchronously  with  a  new 
growth  of  roots  into  the  soil  area  thus  provided  for  root  extension. 

Rust  epidemics  often  attend  the  delayed  ripening  of  cereals,  while  poor 
aeration  resulting  from  a  wet  soil  gives  rise  to  other  diseased  conditions. 
Indigo  wilt  is  caused  by  a  water-logging  of  the  surface  soil  and  consequent 
defective  aeration  (Howard  and  Howard,  1920).  While  an  excess  of  water 
may  produce  yellow,  shrunken  kernels  of  wheat,  etc.,  the  work  of  Harlan 
and  Anthony  (1921)  indicates  that  cereals  are  able  to  utilize  water  up  to 
the  date  of  full  maturity  and  that  a  deficiency  of  water,  even  after  the 
spikelets  are  losing  their  color  results  in  the  checking  of  the  deposit  of  dry 
matter  in  the  grain,  while  a  deficiency  earlier  in  the  development  of  the 
kernel  probably  determines  its  size,  even  before  the  rate  of  deposit  of  dry 
matter  is  checked.  Clearly  the  necessary  water  can  be  applied  more  intelli¬ 
gently  if  a  knowledge  of  the  extent  and  position  of  the  root  system  as 
modified  by  the  chemical  and  physical  nature  of  the  soil  is  known.  De¬ 
creased  yields  can  often  be  correlated  directly  with  conditions  influencing 
the  development  of  the  roots,  and  this  is  especially  true  in  irrigated  districts 
where  water-supply  is  the  great  limiting  factor  to  crop  production.  In  fact, 
root  development  often  explains  the  reasons  for  differences  in  crop  yields 
that  are  otherwise  obscure. 

Roots  of  plants  that  mature  a  crop  in  fairly  dry  soil  must  penetrate 
deeply  and  spread  widely,  a  distribution  hindered  by  a  very  moist  surface 
soil  early  in  the  life  of  the  plant.  One  of  the  most  difficult  problems  of 
irrigation  is  to  apply  the  water  in  such  a  way  that  plants  are  not  made 
surface  feeders  and  the  natural  advantages  of  a  deep  soil  lost  in  consequence. 
Raising  the  water-table  even  temporarily  by  irrigation  causes  death  of 
the  deeper  roots  and  usually  results  in  a  decreased  yield,  although  the 


/ 


Introduction. 


5 


roots  of  some  species  succumb  more  quickly  than  others  (Cannon,  1921). 
In  the  case  of  the  cotton  plant,  Balls  (1919)  has  shown  that  the  amount 
of  shedding  of  leaves  and  bolls  is  proportional  to  the  depth  of  the  root 
system  which  was  submerged  by  a  rising  water-table  (and  soon  died), 
and  that  the  primary  cause  of  shedding  in  Egypt  is  deficient  root  absorption 
due  to  poor  aeration.  This  clearly  illustrates  the  dependence  of  top  devel¬ 
opment  upon  a  sufficient  root-supply.  Howard  (1916),  by  comparing  the 
root-range  and  yield  of  three  varieties  of  gram,  a  legume  widely  grown 
in  India,  found  that  they  yielded  about  the  same  in  a  season  of  good  subsoil 
aeration,  but  during  a  wet  season  the  yield  was  inversely  proportional  to 
the  depth  of  the  root  system,  aeration  playing  the  dominant  role.  The 
importance  of  a  thorough  investigation  of  root  development  and  root  activi¬ 
ties  need  not  be  pointed  out  in  greater  detail  here  (cf.  Weaver,  Jean,  and 
Crist,  1922  :  3). 

The  writers  wish  to  acknowledge  the  faithful  assistance  of  Mrs.  F.  C. 
Jean  in  the  execution  of  the  drawings  of  the  root  systems.  Grateful  acknowl¬ 
edgment  is  made  to  Professor  J.  C.  Russel,  of  the  Department  of  Agronomy 
of  the  University  of  Nebraska,  for  the  generous  use  of  his  laboratories  for 
the  work  on  soil  analyses,  and  to  Dr.  John  W.  Crist  for  analyzing  the  soils 
and  making  nitrate  determinations.  To  Mr.  L.  B.  Werkheiser  we  are 
indebted  for  many  practical  suggestions  in  regard  to  applying  water  in 
irrigation  and  field  management.  It  is  a  pleasure  to  acknowledge  the 
helpful  suggestions  given  by  Dr.  F.  E.  Clements  throughout  the  course 
of  the  work,  and  to  him  and  Professor  T.  J.  Fitzpatrick  the  writers  are 
indebted  for  the  reading  of  the  manuscript. 


6 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 

LOCATION  AND  DESCRIPTION  OF  STATIONS. 

Greeley,  Colorado,  55  miles  north  of  Denver  and  the  center  of  one  of 
the  oldest  irrigated  districts  in  the  State,  was  selected  as  a  suitable  location 
for  the  following  experiments.  This  area  has  been  under  irrigation  since 
1871,  water  being  secured  from  the  mountain  stream,  Cache  La  Poudre, 
a  tributary  of  the  Platte.  It  has  an  elevation  of  4,650  feet  and  a  mean 
annual  precipitation  of  12.7  inches.  Although  about  three-fourths  of  the 
precipitation  occurs  during  the  growing-season,  the  rainfall  is  usually  so 
poorly  distributed  that  dry  farming  is  hazardous.  Moreover,  much  moisture 
is  wasted  in  light  showers,  which  have  little  effect  upon  replenishing  the 
holard,  and  in  torrential  rains  where  run-off  is  very  high.  The  mean 
annual  temperature  is  about  47°  F.  It  increases  gradually  from  48°  F. 
for  April  to  70°  F.  for  August.  The  average  date  of  the  latest  killing  frost 
in  spring  is  May  1  and  of  the  first  killing  frost  in  autumn,  October  1. 
The  sky  is  usually  clear  and  the  per  cent  of  possible  sunshine  very  high 
(66  per  cent,  April  to  September  inclusive,  for  Denver).  Clear,  hot,  dry 
days  are  followed  by  cool  nights  with  marked  rise  in  humidity.  The 
marked  changes  in  day  and  night  temperature  and  humidity  are  well 
illustrated  in  figure  1. 


Fig.  1. — Hygrothermograph  record  for  third  week  in  July,  1923,  showing  usual  wide  fluctuations 
between  day  and  night  temperature  (light  line)  and  humidity  (heavy  line). 

A  station  for  the  growth  of  crops  without  irrigation  was  selected  on  a 
level  tract  of  land  lying  within  the  western  edge  of  the  city.  That  for 
irrigation  was  located  about  a  mile  eastward  and  just  outside  the  city 
limits,  being  under  ditch  No.  3  of  the  Greeley  Irrigation  Company.  It 
was  about  75  feet  lower  than  the  dry-land  station. 

All  the  soils  throughout  the  region  are  of  alluvial  origin  and  consequently 
somewhat  variable  in  texture  and  structure,  even  within  short  distances. 
Hence,  great  care  was  exercised  in  selecting  the  plats  to  secure  as  great  a 
uniformity  as  possible,  and  where  differences  were  found  in  making  the 


Location  and  Description  of  Stations. 


7 


root  excavations  these  have  been  recorded.  The  soil  in  both  areas  con¬ 
sisted  of  a  fine  sandy  loam.  That  in  the  dry  land  was  underlaid  at  a 
depth  of  18  to  24  inches  with  a  very  dry  hard  layer  with  a  sufficiently  high 
lime-content  to  rather  firmly  cement  the  soil  into  a  hardpan  (cf.  Weaver 
and  Crist,  1922).  This  harder  layer  was  usually  10  or  12  inches  thick 
and  gave  way  to  a  looser  soil.  At  a  depth  of  5  or  6  feet  gravel  intermixed 
with  sand  often  occurred,  and  small  rocks  were  not  uncommon  throughout. 
The  soil,  where  dry,  was  so  compact  that  a  trench  could  be  dug  only  with 
the  aid  of  a  large  pick.  In  the  irrigated  plats  the  sandy  loam  was  also 
underlaid  at  a  somewhat  variable  depth  (usually  16  to  24  inches)  by  a 
harder  substratum.  Here  both  the  clay  and  lime  content  increased  rapidly, 
giving  way  again  below  3  feet  to  a  sandier,  less  compact  subsoil.  Below 
4  or  5  feet  pure  sand  or  gravel  and  sand  occurred. 


Table  1. — Mechanical  analyses  of  soils. 


Depth  in  feet. 

Coarse 

gravel. 

Fine 

gravel. 

Coarse 

sand. 

Medium 

sand. 

Fine 

sand. 

Very  fine 
sand. 

Silt. 

Clay. 

Irrigated: 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

0-0.5 . 

0.0 

0.0 

9.3 

11.4 

34.7 

21.7 

12.5 

10.4 

0.5-1 . 

0.0 

0.0 

7.6 

16.7 

37.7 

20.5 

6.1 

11.6 

1-2 . 

0.0 

0.0 

5.0 

12.4 

25.7 

19.7 

16.6 

20.6 

2-3 . 

0.0 

0.0 

5.6 

11.0 

25.4 

22.8 

17.3 

17.9 

3-4 . 

Non-irrigated: 

0.0 

0.0 

8.1 

14.5 

39.9 

21.8 

7.1 

8.4 

0-0.5 . 

0.0 

0.0 

9.3 

10.5 

29.2 

25.0 

11.7 

14.3 

0.5-1 . 

0.0 

0.0 

7.2 

13.4 

36.5 

23.9 

10.4 

8.5 

1-2 . 

0.0 

0.0 

8.0 

10.0 

33.6 

25.2 

10.5 

12.7 

2-3 . 

0.0 

0.0 

7.3 

7.0 

31.4 

26.6 

11.8 

15.9 

3-4 . 

0.0 

0.0 

7.8 

7.8 

32.4 

21.6 

11.4 

19.0 

Physical  analyses  of  the  soil  from  large  composite  samples  for  each  of 
the  several  depths  to  4  feet  in  each  area  are  shown  in  table  1. 


Table  2. — Chemical  analyses  of  soils1 


Depth  in  feet. 

Nitrogen. 

lv20. 

P206. 

Carbon 

dioxide. 

V  olatile 
matter. 

Acidity. 

Irrigated : 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

0-0.5 . 

.051 

1.41 

.109 

.24 

.88 

None. 

0.5-1 . 

.060 

1.29 

.109 

.33 

1.03 

None. 

1-2 . 

.044 

1.30 

.100 

4.39 

1.10 

None. 

2-3 . 

.029 

1.31 

.081 

4.38 

.70 

None. 

3-4 . 

.018 

1.23 

.097 

1.57 

.97 

None. 

Non-irrigated: 
0-0.5 . 

.068 

1.38 

.045 

None 

1.48 

Slight. 

0.5-1 . 

.059 

1.22 

.093 

Trace 

1.36 

Very  slight. 

1-2 . 

.045 

1.24 

.056 

1.94 

1.06 

None. 

2-3 . 

.027 

1.09 

.057 

5.40 

.65 

None. 

3-4 . 

.017 

1.27 

.096 

4.94 

.52 

None. 

1  Nitrogen  was  determined  by  means  of  the  modified  Gunning  method,  K2O  by  fusion  with 
calcium  carbonate,  P2O5  by  digestion  with  aqua  regia,  volatile  matter  by  ignition,  and  replace¬ 
ment  of  inorganic  carbonates  through  the  use  of  (NEbhCCb,  and  acidity  by  the  Truog  method. 


8 


Root  Behavior  and  Crop  Yield  Under  Irrigation . 


There  is  a  distinct  increase  in  both  silt  and  clay  content  of  the  irrigated 
soil  in  the  second  and  third  foot,  with  a  proportional  decrease  in  fine  sand. 
In  fact,  this  layer  might  well  be  designated  as  sandy  clay.  Less  marked 
differences  in  the  clay-content  are  found  in  the  non-irrigated  land,  the 
hardpan  here  being  due  more  largely  to  the  chemical  soil  constituents. 
Chemical  analyses  (table  2)  show  an  abundance  of  carbonates  in  the  second 
and  third  foot.  Here  the  lime  horizon  is  clearly  indicated,  as  well  as  the 
rise  of  the  soluble  salts  as  a  result  of  irrigation. 

An  examination  of  table  2  shows  that  nitrogen  is  low,  while  potash  is 
considerably  higher  than  that  of  the  average  arid  soil.  Phosphorus  is  also 
low,  especially  in  the  non-irrigated  soil.  Considering  the  aridity  of  the 
locality,  the  volatile  matter  is  not  low,  arid  soils  usually  showing  0.85  to 
1  per  cent  for  the  surface  and  0.65  to  0.90  per  cent  for  the  subsoil.  Too 
little  acidity  occurs  at  any  level  to  be  of  any  importance.  In  fact,  analyses 
show  considerable  alkalinity  at  certain  levels. 


\ 


Crops  and  Methods.  9 

CROPS  AND  METHODS. 

The  following  crops  were  grown  for  these  experiments:  Turkestan  alfalfa 
(Medicago  sativa) ,  Marquis  spring  wheat  ( Triticum  aestivum) ,  a  sugar  beet 
of  a  variety  most  commonly  grown  in  the  region,  Klein-wanzleben  ( Beta 
vulgaris),  Bliss’s  Triumph  potato  ( Solanum  tuberosum),  widely  grown  as 
an  early  variety,  and  an  acclimated  yellow  dent  corn,  Minnesota  No.  13 
( Zea  mays  indentata) ,  a  variety  considered  best  adapted  to  the  region. 
Thirtieth-acre  plats  of  each  crop,  exclusive  of  a  discard  area  surrounding 
each,  were  grown  on  the  dry  land  and  in  duplicate  (except  alfalfa)  under 
irrigation.  One  of  the  latter  plats  of  each  crop  was  fully  irrigated1  and  the 
other  watered  less  frequently. 

A  record  of  aerial  environmental  conditions  in  the  two  areas  was  obtained 
largely  by  means  of  recording  instruments,  and  nearly  2,000  soil  samples 
for  holard  determinations  to  depths  of  4  or  more  feet  were  secured.  Also, 
weekly  records  of  soil  temperatures  were  obtained.  To  obviate  local  changes 
in  environment  brought  about  by  the  growth  of  the  crops  (the  plats  of 
beets,  corn,  wheat,  etc.,  each  having  not  only  its  own  partial  environment 
but  one  which  was  constantly  changing)  and  hence  to  more  nearly  compare 
conditions  in  the  two  areas,  a  thirtieth-acre  plat  in  the  center  of  the  fields 
where  the  instruments  were  placed  was  kept  free  from  vegetation.  Friez’s 
hygro thermographs,  placed  in  appropriate  shelters  so  that  the  sensitive 
mechanism  was  about  5  inches  above  the  soil-surface  and  frequently 
checked,  recorded  air-temperature  and  humidity.  The  average  day  tem¬ 
peratures  and  humidities  were  determined  from  the  weekly  record-sheets 
by  adding  the  temperatures  or  humidities  beginning  at  8  a.  m.  and  every  2 
hours  thereafter  until  6  p.  m.  for  each  day  and  dividing  the  sum  by  the  total 
number  of  2-hour  intervals.  Those  for  the  night  intervals  were  calculated 
in  a  similar  manner,  beginning  at  8  p.  m.  and  including  the  readings  until 
6  a.  m.  Evaporation  was  determined  by  Livingston’s  standardized,  spher¬ 
ical,  radio-atmometer  cups,  which  were  run  in  duplicate  and  the  average 
daily  readings  for  each  week  corrected  to  the  standard  cup.  Wind  velocity 
was  not  measured.  In  general,  the  wind  is  high  in  spring  until  about  June  1, 
after  which  it  consists  mostly  of  gentle  breezes.  Soil-temperature  readings 
were  taken  weekly,  the  thermometers  being  inserted  in  the  hole  left  by 
the  Briggs  soil-tube  for  a  period  of  several  minutes  before  each  reading.  In 
addition  to  the  weekly  water-content  detrminations  (100-  to  150-gram 
samples  dried  at  105°  C.  being  used)  to  a  depth  of  4  feet  in  the  uncropped 
areas,  similar  samples  were  taken  at  longer  intervals  in  each  of  the  crop 
plats  from  the  time  of  planting  until  the  crops  were  mature.  At  times  other 
samples  to  the  limit  of  root  penetration,  5  to  9  feet,  were  secured.  All  of 
these  data  are  expressed  in  the  tables  as  water-content  in  excess  of  the 

1  One  of  the  most  important  problems  of  crop  production  under  irrigation  where  an  ever- 
increasing  amount  of  tillable  land  is  placed  under  the  ditch  and  the  supply  of  water  is  limited,  is 
the  proper  use  of  the  latter.  At  present  the  time  of  application  of  irrigation  water  and  the 
amount  used  are  determined  entirely  empirically,  much  water  often  being  wasted,  yields  some¬ 
times  actually  reduced,  and  other  injurious  results  ensuing  from  the  use  of  an  oversupply.  In 
these  experiments  water  was  supplied  at  times  designated  by  the  owner  of  the  land,  a  man  of 
many  years’  experience  in  irrigation,  whose  judgment  in  such  matters  has  been  attested  by  highly 
successful  crop  production. 


10 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


hygroscopic  coefficient  (i.  e.,  approximately  the  water  available  for  growth, 
cf.  Weaver,  1920:28). 

The  amount  of  water  used  in  surface  irrigation  (flooding  in  the  case  of 
wheat  and  alfalfa  and  ditching  in  the  case  of  the  other  crops  planted  in 
rows)  was  not  determined  by  the  usual  method  of  measuring  the  water  per¬ 
mitted  to  flow  upon  the  land  in  acre-inches.  Casual  observation  shows  that 
much  of  this  is  frequently  lost  in  run-off  due  to  variations  in  the  slope  of 
the  land  (the  amount  being  more  or  less  variable,  due  to  the  head  of  water 
used) ,  or  unequally  distributed,  depending  largely  upon  the  original  dryness 
of  the  soil,  its  condition  of  tilth,  etc.  Water-content  was  determined  by 
taking  soil  samples  at  1-foot  intervals  to  depths  of  3  feet  in  the  same  plat 
immediately  preceding  and  following  irrigation,  the  water  penetrating 
readily  because  of  the  sandy  nature  of  the  soil.  By  this  method,  owing 
to  the  large  number  of  samples  taken,  the  actual  increase  in  water-content 
was  ascertained. 

The  method  used  in  excavating  root  systems  was  the  same  as  that 
employed  during  the  past  10  years.  By  the  side  of  the  plants  to  be  exam¬ 
ined,  a  trench  was  dug  to  a  depth  of  about  4  feet  and  of  convenient  width. 
This  affords  an  open  face  into  which  one  may  dig  with  a  hand-pick  and 
other  tools  and  thus  make  a  careful  examination  of  the  entire  root  system. 
This  apparently  simple  process,  however,  requires  much  practice,  not  a  little 
patience,  and  wide  experience  with  soil  texture.  In  every  case  several  plants 
were  examined,  often  10  or  more  at  any  given  stage  of  development,  to 
insure  an  adequate  idea  of  the  general  root  habit.  Among  this  number  it 
was  possible  to  secure  some  root  systems  in  their  entirety.  In  cases  where 
reconstruction  was  necessary,  this  was  rendered  more  accurate  and  less 
difficult  by  methods  of  record  in  the  field.  As  the  work  of  excavation  pro¬ 
gressed,  the  trench  was  deepened,  if  necessary,  so  that  finally  the  soil  under¬ 
lying  the  deepest  roots  was  undercut  for  several  inches  and  carefully 
examined  as  it  was  removed  to  assure  certainty  as  to  the  maximum  depth 
of  the  root-ends.  Frequently  the  trenches  reached  depths  of  5  to  9  feet. 

The  usual  practice  was  followed  of  writing  a  working  description  of  the 
root  system  after  several  plants  had  been  examined  and  then  noting  any 
variation  from  this  description  as  more  roots  were  excavated.  This  check¬ 
ing  of  the  description  in  the  field  leads  to  a  high  degree  of  accuracy,  for 
opportunity  is  offered  for  further  study  if  any  point  regarding  the  root 
habit  remains  indefinite.  This  is  absolutely  essential  in  developmental 
studies.  Drawings  of  the  root  systems  were  made  with  pencil  in  the  field 
on  a  large  drawing-sheet  and  then  retraced  with  India  ink.  They  were 
made  simultaneously  with  the  excavating  of  the  roots  and  always  to  exact 
measurement.  In  the  drawings  the  root  systems  are  arranged  as  nearly  as 
possible  in  the  natural  position  in  a  vertical  plane;  that  is,  each  root  is 
placed  in  its  natural  position  with  reference  to  the  surface  of  the  soil  and 
a  vertical  line  from  the  base  of  the  plant.  In  the  case  of  potatoes  the  roots 
were  so  abundant  that  to  depict  all  of  them  led  to  confusion,  so  that  in  the 
drawings  of  these  plants  only  one-half  of  the  root  system  is  shown. 

In  every  case  it  was  sought  to  illustrate  the  average  condition  of  root 
development  rather  than  the  extreme.  Although  the  drawings  were  made 
on  a  large  scale,  the  rootlets  were  often  so  abundant  that  it  was  quite 


Crops  and  Methods. 


11 


impossible  to  show  the  exact  number  as  determined  by  average  root-counts. 
Such  drawings,  however,  carefully  executed,  represent  the  extent,  position, 
and  minute  branching  of  the  root  system  even  more  accurately  than  a 
photograph,  for  under  the  most  favorable  conditions,  especially  with  exten¬ 
sive  root  systems,  the  photograph  is  always  made  at  the  expense  of  detail, 
many  of  the  finer  branches  and  root-ends  being  obscured. 

The  dry-land  area,  which  produced  no  crop  the  preceding  year,  but  was 
not  entirely  free  from  weeds,  was  plowed  about  8  inches  deep  and  harrowed 
until  a  good  seed-bed  was  formed.  The  irrigated  plats,  upon  which  truck 
crops  were  grown  the  preceding  year,  were  fertilized  uniformly  with  5  tons 
of  barnyard  manure  per  acre,  plowed  9  inches  deep  and  well  harrowed. 


12 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


ENVIRONMENTAL  CONDITIONS,  1922. 

The  aerial  environment  as  regards  temperature  in  the  two  plats  was  not 
greatly  different,  as  may  be  seen  in  table  3. 

May  June  July  August  Sep t 


Fig.  2. — Average  day  temperature  (heavy  lines)  and  average  night  temperature  (light 
lines)  in  dry  land  (solid  lines)  and  irrigated  plats  (broken  lines),  1922. 


The  average  day  and  average  night  temperatures  are  shown  in  figure  2, 
where  it  may  be  seen  that,  except  for  May,  they  are  very  similar.  The 
lower  temperatures  on  the  watered  plats  early  in  the  season  probably 


Table  3. — Average  daily  air  temperatures, 
1922.  ' 


Date. 

Dry 

land. 

Irrigated 

plat. 

°F 

°F 

May  14 . 

67 

54 

21 . 

70 

59 

28 . 

69 

63 

June  4 . 

58 

54 

11 . 

70 

68 

18 . 

74 

71 

25 . 

77 

76 

July  2 . 

77 

75 

9 . 

71 

74 

16 . 

74 

72 

23 . 

74 

76 

30 . 

75 

76 

Aug.  6 .  .  .  . . 

76 

75 

13 . 

75 

75 

20 . 

77 

75 

27 . 

75 

74 

Sept.  3 . 

75 

73 

10 . 

63 

68 

17 . 

62 

64 

Table  4. — Average  day  and  average  night 
humidity,  dry  land,  1922. 


Date. 

Average 

day. 

Average 

night. 

May  28 . 

p.  ct. 

39 

p.  ct. 

66 

June  4 . 

57 

85 

11 . 

49 

60 

18 . 

43 

78 

25 . 

49 

66 

July  2 . 

37 

71 

9 . 

48 

81 

16 . 

38 

63 

23 . 

39 

74 

30 . 

45 

83 

Aug.  6 . 

48 

84 

13 . 

48 

83 

20 . 

48 

90 

27 . 

54 

78 

Sept.  3 . 

45 

80 

10 . 

42 

64 

17 . 

48 

74 

resulted  in  part  from  the  effects  of  irrigation  on  May  15,  much  heat  being 
consumed  in  drying  the  surface  soil.  The  somewhat  higher  night  tempera¬ 
tures  in  the  dry  land  during  the  early  part  of  the  season  are  due  to  cold-air 


Environmental  Conditions,  1922. 


13 


drainage  into  the  irrigated  plats,  which  were  about  75  feet  lower  than  the 
dry  land.  However,  differences  in  temperature  were  so  slight  that  they 
seemed  to  have  little  effect  upon  the  growth  of  the  crops,  especially  after  May. 

The  humidity,  which  during  1922  was  measured  in  the  dry  land  only,  is 
given  in  table  4. 

The  wide  range  between  day  and  night  humidity  is  characteristic  of  the 
Great  Plains  region.  Not  infrequently  the  daily  range  is  through  80  or  90 
per  cent,  humidities  of  10  to  15  per  cent  not  being  uncommon  in  the  after¬ 
noons,  while  at  night  they  often  rise  to  80  or  even  100  per  cent,  owing  to  the 
low  night  temperatures.  The  humidity  was  apparently  somewhat  lower  in 
dry-land  than  in  the  irrigated  plats,  judging  by  the  evaporation  from  the 
black  porous-cup  atmometers  (fig.  3),  which  the  following  season  gave 
almost  identical  losses  at  the  two  stations,  where  the  humidities  were  also 
practically  identical.  Humidity  in  the  irrigated  plats  was  undoubtedly 
increased  not  only  by  the  surface  evaporation  from  the  moister  soil,  but 


Fig.  3. — Average  daily  evaporation  in  dry-land  (solid  line)  and  irrigated  plats  (broken 

line),  1922. 


also  by  the  water  transpired  from  the  luxuriantly  growing  crops.  Moreover, 
in  the  watered  area,  the  uncultivated  plat  where  the  instruments  were  placed 
was  located  in  such  a  manner  that  they  received  the  shade  of  some  black 
locust  trees  at  a  distance  of  80  feet  for  perhaps  an  hour  each  day  just  before 
sunset.  These  trees,  which  were  removed  in  1923,  did  not  come  into  full 
leaf  until  about  the  second  week  in  June.  Aside  from  this,  the  chief  factor 
in  causing  these  differences  in  evaporation  was  greater  wind  movement  in 
the  dry-land  plats,  which  not  only  lay  higher,  but  also  bore  shorter  crops. 
In  addition,  the  irrigated  plats  were  sheltered  on  both  the  west  and  north 
at  no  great  distance  by  a  row  of  trees. 

Soil  temperatures  in  the  two  areas  at  various  depths  were  not  very 
different.  This  may  be  accounted  for  by  the  fact  that  the  irrigation  water, 
although  from  a  mountain  stream,  had  traveled  long  distances  over  the 
broad,  shallow  bed  of  the  river  and  through  the  ditch  until  it  was  quite  as 
warm  as  the  soil  to  which  it  was  applied.  Temperature  variations  were 
most  marked  in  the  surface  3  inches  (fig.  4),  but  no  consistent  differences 
occurred  in  the  two  plats.  Those  at  6  inches  depth  were  usually  2°  to  5°  C. 


14 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


lower  than  at  3  inches,  but  very  similar.  Differences  at  a  depth  of  12  inches 
were  even  less,  the  average  temperature  being  still  lower.  Table  5  shows 


Fig.  4. — Soil  temperature  in  dry-land  (solid  lines)  and  irrigated  plats  (broken  lines), 
at  depths  of  3  inches  (light  upper  lines),  6  inches  (heavy  lines),  and  12  inches  (light 
lower  lines),  1922. 


that  in  the  deeper  soils  (2  to  4  feet)  practically  no  difference  occurred.  It 
is  interesting  to  note  the  rather  low  temperatures  .at  which  deeper  root- 
growth  takes  place. 


Table  5. — Soil  temperatures  in  the  dry-land  and  irrigated  plats ,  1922. 


Date. 

Depth,  2  feet. 

Depth,  3  feet. 

Depth,  4  feet. 

Dry  land. 

Irrigated. 

Dry  land. 

Irrigated. 

Dry  land. 

Irrigated. 

°  C. 

°  C. 

°  C. 

°  C. 

0  C. 

°  C. 

Apr.  20 . 

8.0 

8.5 

8.0 

8.0 

8.0 

8.0 

24 . 

10.0 

10.0 

9.0 

9.0 

8.0 

8.0 

May  1 . 

10.0 

10.0 

9.0 

9.0 

9.0 

9.0 

8 . 

15.0 

13.5 

13.0 

13.0 

10.5 

11.5 

15 . 

12.5 

14.0 

11.0 

13.0 

10.5 

11.0 

22 . 

17.5 

17.0 

16.0 

16.0 

13.0 

13.0 

29 . 

18.0 

17.0 

15.5 

15.0 

15.0 

14.0 

June  5 . 

17.0 

16.5 

15.0 

15.0 

13.0 

15.0 

12 . 

21.0 

22.0 

18.0 

19.0 

16.0 

17.5 

19 . 

23.0 

25.0 

20.0 

23.5 

17.5 

20.5 

26 . 

24.5 

22.0 

22.0 

20.0 

19.0 

19.0 

July  3 . 

24.0 

21.5 

22.0 

20.0 

21.0 

18.5 

24 . 

22.5 

22.0 

21.0 

21.0 

20.0 

19.5 

Aug.  28 . 

23.0 

24.0 

22.0 

23.0 

21.0 

22.0 

Summarizing,  air  temperatures  on  the  dry  land  were  very  similar  to  those 
in  the  watered  area,  except  in  May,  when  they  were  2°  to  6°  F.  higher.  Soil 
temperatures  at  all  depths  were  almost  identical.  Humidity  was  a  little 
lower  in  the  drier  area,  wind  movement  somewhat  greater,  and  evaporation 
higher,  all  of  these  not  only  contributing  to  greater  water-loss  directly  from 
the  soil,  but  also  accelerating  transpiration. 


15 


Experiments  With  Alfalfa. 

EXPERIMENTS  WITH  ALFALFA. 

Turkestan  alfalfa  was  drilled  an  inch  deep  and  in  rows  20  inches  apart 
in  the  dry-land  plat  at  the  rate  of  15  pounds  per  acre  on  April  11.  Seed 
was  also  sown  broadcast  at  a  similar  rate  and  at  the  same  time  in  the  irri¬ 
gated  plat,  being  worked  into  the  soil  by  the  use  of  a  hand  rake.  A  fine 
moist  seed-bed  at  both  stations  resulted  from  a  snow  which  fell  on  April  16. 


Fig.  5. — A  and  B,  roots  of  alfalfa  plants  2  months  old,  those  in  dry  land  with 
greater  depth  and  longer  branches;  C  and  D,  plants  3  months  old,  the 
one  from  the  dry  land  having  the  greater  number  of  branches. 


16 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


The  drilled  dry-land  plat  was  hoed  at  frequent  intervals  throughout  the 
season  to  conserve  the  moisture,  but  the  irrigated  plat  was  not  tilled,  the 
weeds  merely  being  pulled  from  time  to  time. 

Owing  to  favorable  temperatures,  the  crop  grew  well,  and  on  June  10, 
60  days  after  the  seed  was  sown,  it  had  reached  a  height  of  about  3  inches 
in  the  dry  land  and  6  inches  in  the  irrigated  field,  the  plants  in  both  plats 
being  furnished  with  6  to  8  leaves.  Root  excavations  at  this  time  showed 
rather  marked  differences  in  the  branching  habit,  as  well  as  depth  of  pene¬ 
tration  (fig.  5,  a,  b). 

Alfalfa  is  characterized  by  a  strong  tap-root  which  penetrates  rather 
vertically  downward,  its  course  in  dry,  hard  soil  often  being  somewhat 
tortuous.  Plants  in  the  dry  land  had  reached  depths  of  18  to  27  inches, 
which  was  4  to  5  inches  deeper  than  in  the  irrigated  plats.  The  number  of 
laterals  (about  6  per  inch)  was  less  in  the  drier  soils,  but  they  were  longer. 
In  the  irrigated  plats  they  were  mostly  less  than  2  inches  long,  but  in  the 
dry  land  many  were  3  inches  and  some  as  much  as  7  inches  in  length. 

Table  6. — Holard  in  excess  of  the  hygroscopic  coefficient  in  uncropped  areas  at  the  two  stations, 

1922} 


Date. 

Dry-land  plat,  depth  in  feet. 

Irrigated  plat,  depth  in  feet. 

0  to  0.5 

0.5  to  1 

1  to  2 

2  to  3 

3  to  4 

0  to  0.5 

0.5  to  1 

1  to  2 

2  to  3 

3  to  4 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

Apr.  19 . 

6.7 

3.5 

1.1 

4.5 

4.9 

6.4 

10.2 

12.8 

12.2 

10.5 

24 . 

4.6 

3.4 

0.0 

0.4 

3.5 

6.1 

4.6 

10.5 

10.3 

6.2 

May  1 . 

9.1 

7.3 

5.6 

2.3 

2.8 

6.3 

8.5 

5.8 

12.1 

5.6 

8 . 

3.9 

3.6 

3.8 

-1.4 

3.9 

5.3 

8.9 

13.1 

10.0 

6.0 

15 . 

5.9 

5.0 

3.1 

-0.3 

4.6 

4.9 

8.4 

13.2 

9.0 

8.0 

15 . 

(9.0) 

(9.0) 

(0.8) 

(3.3) 

22 . 

3.2 

3.9 

2.6 

-1.4 

4.8 

6.7 

8.8 

10.9 

12.0 

7.0 

29 . 

2.7 

3.4 

2.6 

-1.5 

-1.3 

6.6 

8.8 

11.7 

12.8 

5.6 

June  5 . 

3.0 

2.9 

3.1 

-0.5 

-0.7 

6.4 

8.5 

9.5 

11.4 

3.1 

12 . 

2.4 

3.2 

3.4 

-1.1 

-2.1 

3.9 

9.0 

12.8 

12.2 

6.1 

19 . 

1.8 

1.6 

2.8 

-1.4 

-1.7 

-0.6 

2.7 

15.2 

14.5 

4.8 

19 . 

(13.3) 

(13.3) 

(4.7) 

(0.0) 

26 . 

0.7 

1.5 

2.7 

-1.7 

-2.2 

5.9 

11.8 

11.7 

10.5 

4.9 

July  24 . 

-0.2 

1.9 

-0.2 

-1.2 

-0.8 

2.4 

10.8 

11.1 

11.4 

3.8 

31 . 

1.5 

1.1 

1.9 

-0.8 

-1.3 

4.4 

9.7 

12.4 

11.0 

3.5 

Aug.  7 . 

3.2 

2.1 

2.6 

-0.1 

-0.8 

4.0 

6.9 

11.3 

11.7 

12.3 

28 . 

0.4 

-0.8 

1.5 

-1.1 

0.0 

5.4 

8.9 

12.7 

11.0 

8.2 

Hygroscopic  coeffi- 

cient . 

4.2 

5.4 

4.4 

4.3 

5.6 

4.6 

4.9 

8.0 

6.8 

4.0 

1  Figures  in  parentheses  in  all  of  the  tables  indicate  the  increase  in  water-content  due  to  irriga¬ 
tion. 

Secondary  branches  were  more  abundant  in  the  dry  land,  as  were  root 
tubercles  also.  These  differences  may  be  largely  if  not  entirely  attributed 
to  differences  in  soil  moisture.  In  the  dry  land  the  first  foot  of  soil  had 
about  5  per  cent  chresard  on  April  19,  but  this  was  rather  gradually  depleted 
(table  6)  until,  at  the  time  of  the  root  examinations,  none  occurred  in  the 
first  6  inches  and  only  3  or  4  per  cent  to  the  depth  of  root  penetration 
(table  7). 


Experiments  With  Alfalfa. 


17 


Available  water  in  the  irrigated  plats  was  about  8  per  cent  on  April  19 
and  the  crop  was  furnished  with  an  abundant  supply  on  May  12  (table  7) 
and  at  the  time  of  root  examinations  3  to  13  per  cent  was  available. 


Table  7. — Holard  of  alfalfa  plats  in  excess  of  hygroscopic  coefficient,  1922. 


Date. 

Dry  land,  depth  in  feet. 

Fully  irrigated,  depth  in  feet. 

0  to  0.5 

0.5  to  1 

1  to  2 

2  to  3 

3  to  4 

0  to  0.5 

0.5  to  1 

1  to  2 

2  to  3 

3  to  4 

Apr.  19 . 

May  12 . 

p.  ct. 
6.7 

p.  ct. 
3.5 

p.  ct. 
1.1 

p.  ct. 
4.5 

p.  ct. 
4.9 

p.  ct. 

6.4 
-0.7 

(6.4) 

2.5 
(7.0) 
2.4 
(7.8) 

1.9 

0.0 

p.  ct. 
10.2 
0.0 
(6.4) 

3.7 
(7.0) 
4.4 
(8.0) 

4.8 
0.0 

p.  ct. 
12.8 
8.9 
(3.9) 
12.5 
(2.8) 
8.2 
(1.6) 
7.1 
5.3 

p.  ct. 
12.2 
12.5 
(2.8) 
9.4 
(5.2) 
7.2 
(6.5) 
9.4 
7.6 

p.  ct. 
10.5 

12 . 

June  10 . 

10 . 

0.0 

3.0 

4.5 

June  28 . 

28 . 

July  8 . 

Sept.  12 . 

Hygroscopic  coeffi¬ 
cient . 

0.0 

0.0 

1.5 

0.6 

2.4 

0.1 

3.5 

0.9 

2.4 

5.4 

4.2 

5.4 

4.4 

4.3 

5.6 

5.5 

8.1 

8.0 

4.5 

2.3 

Practically  no  efficient  rainfall  occurred  to  July  8,  when  the  root  develop¬ 
ment  was  again  examined.  A  glance  at  table  6  shows  that  the  soil  moisture, 
even  in  the  uncropped  area,  had  gradually  been  depleted,  while  in  the 
alfalfa  plat  there  was  practically  none  available  in  the  surface  foot,  and 
only  2  or  3  per  cent  remained  in  the  deeper  layers  (table  7).  Good  moisture 
conditions  had  been  maintained  in  the  irrigated  plat  by  flooding  on  June  28. 
The  plants  were  now  nearly  3  months  old.  Those  in  the  watered  plat  were 
18  inches  in  average  height  and  many  were  in  blossom.  In  the  dry  land 
they  were  only  half  as  tall  and,  while  some  were  in  blossom  and  a  few  in 
fruit,  most  of  them  had  not  bloomed. 

Even  a  glance  at  figure  5,  c,  d,  shows  marked  differences  in  the  root 
habit.  The  prominence  of  the  tap-root,  its  greater  depth  of  penetration, 
and  the  relative  scarcity  of  large  branches  characterized  the  plants  in  the 
moist  soil.  This  is  the  rooting  habit  characteristic  of  alfalfa  (cf.  Weaver, 
Jean,  and  Crist,  1922:  52).  This  contrasted  sharply  with  the  shallower, 
more  profusely  branched  tap-root  found  in  the  dry  land,  where  several  of 
the  major  branches  frequently  reached  depths  nearly  or  quite  as  great  as 
the  main  root.  A  similar  root  habit  has  been  determined  in  the  dry  land 
at  Burlington,  Colorado,  where  the  available  soil  moisture  was  also  largely 
confined  to  the  surface  2  feet  (1.  c.,  p.  69).  While  most  of  the  dry-land 
plants  gave  off  from  3  to  6  large  branches  in  the  first  foot  of  soil,  about  half 
of  the  plants  in  moist  soil  had  none,  and  many  had  only  one,  although  some, 
especially  isolated  individuals,  frequently  had  2  or  more.  Moreover,  there 
was  a  greater  tendency  for  the  branches  in  dry  land  to  turn  downward  with 
less  lateral  spread  than  in  moist  soil.  The  number  of  small  laterals  (6  to 
10  per  inch)  was  about  the  same  in  both  cases,  although  they  extended  much 
closer  to  the  root-tips  in  the  dry  soil,  undoubtedly  because  of  the  slower 


18  Root  Behavior  and  Crop  Yield  Under  Irrigation. 

elongation  of  the  main  roots.  In  the  irrigated  plats  the  tap-roots  had  grown 
at  an  average  rate  of  about  0.5  inch  per  day,  some  reaching  depths  of  over 


Fig.  6. — Alfalfa  near  the  end  of  the  first  season’s  growth:  A,  dry  land;  B,  irrigated  soil. 

3  feet.  Nodules  1  to  2  mm.  in  diameter  occurred  abundantly  over  the  entire 
root  system  of  irrigated  plants,  but  in  the  dry  land  they  were  smaller,  not 


Experiments  With  Alfalfa. 


19 


abundant,  and  fairly  well  distributed  only  in  the  first  18  inches  of  soil. 
Thus  it  seems  clear  that  the  unfavorable  environment  not  only  affects  crop 


Fig.  7. — Root  system  of  alfalfa  on  July  2  of  second  year  of  growth:  A, 

dry  land;  B,  irrigated  soil. 

growth  directly,  but  also  indirectly  through  its  influence  upon  the  nodule¬ 
forming  as  well  perhaps  as  other  types  of  nitrogen-fixing  bacteria. 


20 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


A  final  examination  of  the  growth  of  the  plants  was  made  on  September 
12.  Rainfall  since  July  8  had  been  very  light  (table  8),  much  of  the 
moisture  having  been  dissipated  in  light  showers.  Water,  even  in  the 


Table  8. — Mean  monthly  'precipitation  and  precipitation  in  1922  and  1923 ,  in  inches. 


Month. 

Average, 
33  years. 

1922. 

1923.  Month. 

Average, 
33  years. 

1922. 

1923. 

.Tan . 

0.29 

0.29 

0.07  July . 

1.87 

1.46 

.69 

Feb . 

.42 

.36 

1 . 39  Aug . 

1.06 

1.72 

1.80 

Mar  . 

.76 

.15 

2.12  Sept . 

1.02 

.05 

Apr 

1.72 

1.73 

.82  Oct . 

.96 

.02 

May . 

2.50 

1.25 

2.14  Nov . 

.33 

.61 

.Tune . 

1.40 

.25 

4.58  Dec . 

.41 

.43 

Annual . 

12.76 

8.32 

uncropped  dry-land  area,  was  very  scarce,  while  in  the  alfalfa  field  prac¬ 
tically  none  was  available  above  the  3-foot  level,  and  only  3  per  cent  in 
the  fourth  and  fifth  foot.  A  deficiency  also  occurred  in  the  surface  foot  of 
the  other  plat,  which  had  not  been  watered  since  June  28,  but  the  deeper 
soils  at  least  to  5  feet  had  5  to  8  per  cent  of  chresard. 

In  the  irrigated  plats  the  crop  was  26  inches  high  and  blooming  profusely ; 
this  was  a  second  growth,  a  first  cutting  having  been  made  on  July  26,  when 
the  plants  were  in  bloom  and  20  inches  tall.  In  the  dry  land,  where  it  had 
also  been  cut  on  July  26  when  9  inches  tall,  it  was  only  8  inches  in  average 
height.  The  working-depth  of  the  roots  (i.  e.,  depths  to  which  many  of  the 
roots  penetrated  and  to  which  level  much  absorption  took  place)  was  4.6 
and  3.2  feet  in  the  irrigated  and  dry-land  plats  respectively  (fig.  6).  In  the 
irrigated  field  the  strong  tap-roots,  now  3  to  10  mm.  in  diameter,  with  their 
characteristic  vertical  penetration,  had  reached  a  maximum  depth  of  6.1 
feet  where  the  soil  was  filled  with  seepage  water.  Those  in  the  dry  land, 
while  similar  in  this  general  habit,  were  much  more  kinked  and  curved,  prob¬ 
ably  owing  to  the  difficulty  in  penetrating  the  hard,  dry  soil,  and  none 
extended  deeper  than  5.5  feet,  since  below  this  the  soil  was  dry.  The  strong 
lateral  branches,  from  2  to  9  in  number,  arose  almost  invariably  in  the  first 
foot  of  soil,  in  some  cases  branching  being  so  profuse  that  the  tap-root 
diminished  in  size  so  rapidly  as  to  be  scarcely  distinguishable  from  the 
branches.  They  seldom  spread  over  6  to  8  inches  laterally  before  they 
turned  downward  and  penetrated  deeply.  But  on  the  irrigated  plants  rarely 
more  than  4  or  5  large  branches  occurred,  and  although  they  usually 
originated  in  the  shallower  soils,  they  not  infrequently  arose  at  greater 
depths.  Their  spread  was  much  more  pronounced,  sometimes  reaching  2 
feet.  As  before,  little  difference  was  noted  in  the  number,  length,  or  branch¬ 
ing  of  smaller  laterals,  which  were  now  well  furnished  with  branches  of  a 
lower  order.  While  no  nodules  were  found  in  the  dry-land  plants,  they  were 
abundant  to  a  depth  of  over  4  feet  on  roots  in  the  irrigated  soil.  The  yield 
of  the  crop  in  tons  per  acre  for  the  first  cutting  on  July  26  was  0.12  on  the 
dry  land  and  0.52  on  irrigated  soil  (cf.  plate  1,  a). 


21 


Experiments  With  Wheat. 


EXPERIMENTS  WITH  WHEAT. 

Marquis  spring  wheat  was  drilled  at  a  depth  of  2  inches  in  rows  8  inches 
apart  at  the  rate  of  90  pounds  per  acre  in  both  dry  and  irrigated  land  on 
April  1.  No  efficient  moisture  fell  until  April  16,  and  hence  the  crop  germi¬ 
nated  and  grew  slowly.  The  chresard  in  the  dry  land  was  practically  nil  in 
the  second  foot  of  soil  during  April  (table  6),  but  in  the  irrigated  plats  a 
good  water-content  prevailed  to  May  10,  the  time  of  the  first  examination. 

The  crops  in  both  areas  were  now  4.5  inches  high,  the  parent  plants  having 
about  4  leaves  each  and  2  tillers.  The  number  of  roots  varied  from  4  to  7 
in  both  plats.  Their  characteristic  spreading  habit  is  shown  in  figure  8,  a,  b, 
together  with  the  branching  and  depth  of  penetration.  The  roots  had  grown 
more  rapidly  in  the  soil  of  the  irrigated  plats  (about  0.5  inch  per  day), 
where  they  showed  the  usual  penetration  and  branching  (cf.  Weaver,  Jean, 
and  Crist,  1922  :  49),  reaching  maximum  depths  of  23  inches  as  compared 
with  18  inches  in  the  dry  land ;  3  to  6  inches  of  the  tips  in  the  first  case,  but 
only  1  or  2  in  the  latter,  were  devoid  of  branches.  Although  the  number  of 
branches  was  about  the  same  in  both  cases,  they  averaged  considerably 
longer  in  the  dry-land  plat. 


Table  9. — Holard  of  wheat  plats  in  excess  of  the  hygroscopic  coefficient,  1922. 


Date,  etc. 

0  to  0.5 
foot. 

0.5  to  1 
foot. 

1  to  2 
feet. 

2  to  3 
feet. 

3  to  4 
feet. 

Dry  land: 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

Apr.  19 . 

6.7 

3.5 

1.1 

4.5 

4.9 

May  22 . 

1.9 

3.4 

4.7 

3.8 

5.1 

June  9 . 

0.2 

2.0 

5.7 

2.7 

July  7 . 

1.0 

0.3 

2.7 

"  3.5 

Hyg.  coef . 

4.2 

5.4 

4.4 

4.3 

5.6 

Lightly  irrigated: 

Apr.  19 . 

6.4 

10.2 

12.8 

12.2 

10.5 

May  17 . 

0.0 

-0.1 

7.1 

12.6 

May  22 . 

0.2 

2.1 

7.0 

10.8 

5.1 

June  9 . 

0.2 

1.7 

8.4 

10.3 

4.4 

June  9 . 

June  28 . 

(18.7) 

-0.1 

(18.9) 

-0.2 

(10.1) 

9.4 

(5.0) 

11.5 

June  28 . 

July  7 . 

(16.8) 

3.1 

(16.0) 

5.1 

(5.0) 

12.7 

(1.1) 

11.5 

5.9 

Hyg.  coef . 

5.5 

8.1 

8.0 

4.5 

2.3 

Fully  irrigated: 

Apr.  19 . 

5.9 

11.1 

12.0 

11.9 

10.8 

May  17 . 

0.2 

0.2 

2.6 

3.4 

May  17 . 

May  22 . 

(20.0) 

4.2 

(20.0) 

4.3 

(11.4) 

3.9 

(11.1) 

6.2 

7.2 

June  9 . 

0.4 

0.6 

0.4 

3.5 

5.1 

June  9 . 

June  21 . 

(14.1) 

0.0 

(14.1) 

0.1 

(12.6) 

1.9 

(5.7) 

3.6 

4.9 

June  21 . 

June  28 . 

(18.8) 

1.2 

(18.8) 

1.0 

(14.2) 

3.7 

(14.0) 

4.0 

6.4 

June  28 . 

July  7 . 

(12.5) 

0.0 

(12.4) 

1.7 

(11.7) 

2.8 

(3.0) 

4.4 

7.9 

Hyg.  coef . 

3.5 

3.7 

3.5 

3.2 

2.8 

A  second  study  of  root-growth  was  made  a  month  later  on  June  7-9.  Only 
1.25  inches  of  rain  fell  during  this  interval  and  the  dry-land  soil  was  con¬ 
stantly  at  a  low  water-content,  although  since  May  some  moisture  was 
available  in  the  second  as  well  as  the  first  foot  (table  9).  No  water  had 


22 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


yet  been  added  to  the  lightly  irrigated  plat,  but  its  water-content  had  been 
constantly  higher  than  on  the  dry  land.  The  third  plat  had  been  irrigated 
on  May  17  (table  9).  The  crops  in  the  dry-land,  lightly  irrigated,  and 
fully  irrigated  plats  respectively  were  13,  19,  and  21  inches  in  average 
height,  the  average  length  of  leaves  being  4,  5,  and  6.5  inches.  While  only 
1  to  2  tillers  per  plant  occurred  in  the  dry  land,  2  or  3  were  usual  in  the  other 
plats.  The  dry-land  crop  showed  distinct  signs  of  suffering  from  drought. 


Fig.  8. — Roots  of  wheat:  A  and  B,  6  weeks  old,  the  former  in  soil  where  little  water  occurred 
in  the  second  foot:  C,  D,  and  E,  2.5  months  old  in  dry  land,  lightly  irrigated  (more 
clayey)  and  fully  irrigated  (sandier)  soils  respectively. 

The  root  habit  in  the  three  plats  was  very  different,  as  may  be  seen  in 
figure  8,  c,  d,  and  e.  The  larger  roots,  which  were  4  to  8  in  number  in  the 
drier  soils,  were  slightly  fewer  in  the  fully  irrigated  plat,  where  they  also 
spread  less  widely  (according  to  normal  habit) ,  but  penetrated  much  deeper 
in  the  sandy  soil.  The  maximum  depth  of  penetration  in  the  several  plats, 


Experiments  With  Wheat. 


23 


beginning  with  dry  land,  was  31,  41,  and  65  inches  respectively.  In  dry  land 
the  roots  often  spread  horizontally  a  few  inches  below  the  soil  surface  for  dis¬ 
tances  of  6  to  10  inches,  others  reached  a  similar  lateral  spread  at  depths 
of  only  6  or  8  inches,  thus  securing  the  water  furnished  by  showers,  and 
some  grew  rather  vertically  downward.  All  showed  by  their  meandering 
course  the  difficulty  of  penetrating  the  compact  soil.  In  irrigated  soil  the 
lateral  spread  was  much  less  pronounced.  However,  except  for  a  greater 
length  of  unbranched  root-ends  in  moist  soil,  the  rate  of  branching  (8  to  12 
per  inch)  was  not  greatly  different.  But  the  branches  became  longer  as  the 
soil  became  drier  and  the  supply  of  tertiary  branches,  which  was  practically 
nil  in  the  moist  soil,  became  pronounced.  In  all  the  plats  the  plants  had 
put  forth  fine  roots  which  ran  almost  horizontally  in  the  surface  soil.  In 
many  instances,  more  especially  in  the  drier  plats,  some  of  these  had  grown 
but  a  few  inches  and  died.  It  seems  that  this  root-growth  had  been  stimu¬ 
lated  by  rains  (or  irrigation) ,  some  of  the  roots  which  had  failed  to  penetrate 
deeper  dying  as  the  holard  was  lost  by  evaporation.  Great  mats  of  these 
roots,  especially  long  and  branched  in  the  dry  land,  filled  the  furrow  slice. 
The  presence  of  a  clayey  subsoil  below  the  surface  10  inches  of  sandy  loam 
in  the  lightly  irrigated  plat  may  have  accounted  in  part  for  the  reduced 
penetration  of  the  root  system  here,  as  compared  with  the  fully  irrigated 
plat  where  the  soil  was  sandy  throughout. 

The  third  examination  was  made  a  month  later,  on  July  5  to  7,  when  the 
crops,  now  96  days  old,  were  nearly  ripe.  The  very  meager  rainfall  during 
this  interval  was  entirely  dissipated  in  several  light  showers,  and  the  soil 
in  the  dry  land  had  become  progressively  drier  (table  6).  The  water-content 
in  the  several  wheat  plats  is  given  in  table  9.  The  lightly  irrigated  plat  had 
been  watered  on  June  9  and  28  and  the  fully  irrigated  one  in  addition 
on  June  21.  The  crop  in  the  dry  land  was  onty  15  inches  high,  perhaps  half 
of  the  plants  only  being  furnished  with  a  tiller,  very  few  of  which  headed 
(plate  2a).  In  the  lightly  irrigated  plat  the  crop  was  41  inches  tall,  mostly 
1,  but  very  frequently  2,  tillers  per  plant  with  heads  occurring,  while  in  the 
heavily  irrigated  field  2  tillers  with  heads  predominated,  although  many 
plants  had  but  1.  The  average  height  was  43  inches  (plate  2b). 

Differences  in  root  habit  were  quite  as  marked  as  at  the  preceding  exami¬ 
nation  (fig.  9).  A  comparison  of  figures  8  and  9  shows  that  the  roots  in  the 
dry  land  had  grown  relatively  little  during  the  month,  the  chief  difference 
being  a  more  thorough  occupation  of  the  second  and,  to  a  slight  extent,  the 
third  foot  of  soil.  The  working  depth  was  24  inches  as  compared  with  36 
and  52  inches  in  the  lightly  and  fully  watered  plats  respectively.  In  the 
same  sequence  the  maximum  depths  of  penetration  were  37,  55,  and  75 
inches.  As  before,  the  lateral  spread  was  greatest  in  dry  land.  The  plants 
in  all  the  plats  were  similar  in  having  a  large  number  of  superficial  roots 
arising  from  the  nodes  above  the  hypocotyl  and  spreading  widely  in  a  rather 
horizontal  position  so  as  to  thoroughly  occupy  the  furrow  slice.  Probably 
owing  to  the  death  by  drought  of  many  of  these  roots  in  the  drier  plats,  they 
were  more  abundant  and  also  longer  in  the  fully  irrigated  one.  Here  they 
extended  outward  to  distances  of  10  to  14  inches.  These,  with  the  profusely 
branched  older  roots,  formed  a  wonderfully  efficient  absorbing  system. 
Although  little  or  no  difference  in  the  number  of  primary  branches  on  the 


24 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


larger  roots  was  determined,  the  smaller  growth  of  these  in  length  as  the 
soils  grew  wetter  was  very  marked,  those  in  the  best  watered  soils  being 


Fig.  9. — Roots  of  wheat  at  maturity:  A,  dry  land;  B,  lightly  irrigated;  and  C,  fully 

irrigated  soil,  1922;  D,  dry  land,  1923. 


Experiments  With  Wheat 


25 


usually  only  about  an  inch  long.  Moreover,  they  had  relatively  few  sec¬ 
ondary  and  tertiary  branches  compared  with  the  densely  rebranched  roots 
in  the  dry  land.  These  differences  in  number  and  length  of  branches  were 
clearly  marked,  even  among  the  plants  of  the  fully  and  lightly  watered  soil. 
Owing  to  the  sandier  soil  in  the  fully  irrigated  plat  (nearly  pure  sand  below 
the  furrow  slice)  the  yield,  which  was  at  the  rate  of  29  bushels  per  acre, 
was  3  bushels  less  than  in  the  lightly  watered  but  more  clayey  soil,  but  that 
in  the  dry  land  was  only  3  bushels  per  acre.  The  total  dry  weight  in  tons 
per  acre  in  the  above  sequence  was  2.9,  3.4,  and  0.4  respectively  (plate  1,  b). 


26 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


EXPERIMENTS  WITH  SUGAR  BEETS. 

Klein-wanzleben  sugar  beet  was  drilled  one  inch  deep  on  April  12  in  rows 
18  inches  apart  in  the  seed-bed  earlier  prepared.  Similar  seeding  but  1.5 
inches  deep  was  done  on  the  dry-land  plats  at  the  same  time.  On  May  26 
the  crop  was  thinned  so  that  the  plants  were  12  inches  apart  in  the  rows. 
The  plats  were  also  subjected  to  shallow  cultivation  at  this  time  and  on 
several  other  occasions  during  the  earlier  part  of  their  growth.  The  water- 
content  to  the  time  of  the  first  root  excavations  on  June  7-9  may  be  found 
in  table  10. 


Table  10. — Holard  of  beet  plats  in  excess  of  hygroscopic  coefficient ,  1922. 


Date,  etc. 

0  to  0.5 
foot. 

0.5  to  1 
foot. 

1  to  2 
feet. 

2  to  3 
feet. 

3  to  4 
feet. 

Dry  land: 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

Apr.  19 . 

6.6 

3.3 

1.3 

4.4 

4.6 

May  8 . 

3.9 

3.8 

3.4 

0.1 

3.8 

29 . 

2.7 

3.4 

•  2.6 

-1.5 

-1.3 

June  12 . 

5.4 

8.2 

6.0 

July  8 . 

2.1 

3.8 

2.4 

1.5 

Sept.  13 . 

-0.7 

0.8 

1.5 

0.9 

4.0 

Hygro.  coef . 

4.2 

5.4 

4.4 

4.3 

5.6 

Lightly  irrigated: 

Apr.  19 . 

6.0 

10.3 

12.4 

12.0 

10.8 

May  8 . 

5.3 

8.4 

12.9 

10.5 

6.1 

29 . 

6.6 

8.8 

11.6 

12.7 

5.4 

June  12 . 

3.9 

9.0 

12.8 

12.2 

6.1 

July  8 . 

0.2 

2.7 

8.2 

6.2 

5.3 

15 . 

—  1.1 

-1.4 

-0.4 

3.5 

15 . 

(20 . 0) 

(20.2) 

(14.1) 

(1.9) 

Aug.  19 . 

0.1 

-0.2 

3.3 

9.5 

19 . 

(13.0) 

(13.3) 

(8.5) 

(2.2) 

Sept.  13 . 

0.5 

2.6 

9.4 

11.0 

14.2 

Hygro.  coef . 

4.6 

4.9 

8.0 

6.8 

4.0 

Fully  irrigated: 

Apr.  19 . . 

5.2 

10.1 

10.4 

10.1 

11.3 

May  8 . 

5.7 

8.5 

12.6 

10.0 

6.0 

29 . 

6.3 

8.4 

11.9 

12.4 

4.8 

June  12 . 

4.0 

9.6 

12.3 

12.0 

5.1 

28 . 

2.6 

1.4 

2.5 

4.5 

5.3 

28 . 

(16.3) 

(16.0) 

(10.4) 

(2.8) 

July  8 . 

3.3 

7.8 

10.9 

6.0 

9.1 

22 . 

1.1 

0.9 

0.6 

5.9 

< 

22 . 

(14.7) 

(14.5) 

(15.1) 

(8.8) 

Aug.  19 . .  . 

2.6 

2.4 

7.5 

11.6 

19 . 

(10.5) 

(10.4) 

(3.8) 

(3.9) 

Sept.  13 . 

0.8 

4.8 

8.6 

12.6 

16.1 

Hygro.  coef . 

3.5 

3.7 

3.5 

3.2 

2.8 

The  chresard  was  much  more  favorable  in  the  irrigated  plats,  although 
no  water  had  been  added.  Although  the  plants  were  slightly  less  than  2 
months  old,  they  had  from  8  to  10  leaves  each.  Those  in  the  dry  land  were 
about  4  inches  tall,  while  in  the  irrigated  area  they  averaged  an  inch  higher. 

As  is  well  known,  sugar  beets  are  characterized  by  a  strong  tap-root  (fig. 
10).  Striking  differences  in  size,  depth  of  penetration,  and  branching  habit 
occurred  in  the  different  plats.  Those  in  the  dry  land  averaged  about  5  mm. 
in  diameter,  while  in  the  irrigated  plats  this  was  nearly  2  mm.  greater.  They 
tapered  off  rapidly  and  in  descending  3  or  4  inches  lost  half  of  their  width. 


Experiments  With  Sugar  Beets. 


27 


A  maximum  depth  of  only  14  inches  was  found  in  dry  land,  where  prac¬ 
tically  no  water  was  available  in  the  second  foot  during  April  and  very  little 
during  May,  and  28  inches  in  the  irrigated  plats,  where  the  root  could 


Fig.  10. — Sugar  beets  about  2  months  old:  A,  dryland  (practically  no 
chresard  in  second  foot);  B,  irrigated  soil,  1922. 

develop  more  normally.  Just  below  the  soil  surface  and  for  a  distance  of 
2  to  4  inches,  laterals  occurred  in  two  rows  on  opposite  sides  of  the  root. 
They  were  grouped  in  clusters  of  2  to  4.  They  seldom  exceeded  1.5  inches 
in  length,  but  this  root  zone  was  more  extensive  (about  4  inches  long)  on 
the  larger  roots  in  the  moister  soil.  Larger  branches  originating  from  all 
sides  of  the  root  occurred  in  the  deeper  soils,  extending  much  nearer  to  the 
end  of  the  tap-root  in  the  dry  land.  Here  they  were  1  to  7  inches  in  length, 
the  longer  ones  being  profusely  rebranched,  while  in  the  irrigated  soil  they 
were  not  only  much  shorter  (2.5  inches  or  less) ,  but  were  very  poorly  fur¬ 
nished  with  laterals.  Moreover,  these  primary  branches  were  less  numerous 
(6  to  8  per  inch)  than  in  dry  land,  where  8  to  12  occurred  regularly  on  an 
inch  of  tap-root.  Differences  in  lightly  and  fully  irrigated  soil  consisted  of 
lateral  branches  on  the  roots,  in  the  former  being  somewhat  more  numerous 
and  their  sublaterals  longer.  Thus  these  white,  succulent,  rather  tender 
beet  roots  are  considerably  modified  by  environment. 

Excavations  were  again  made  and  the  roots  examined  just  a  month  later, 
on  July  7-8.  As  already  stated,  no  efficient  rainfall  occurred  during  this 
period  and  the  soil  became  almost  depleted  of  available  water  in  the  dry 
land,  where  only  2  to  4  per  cent  remained  to  a  depth  of  3  feet  (table  10). 
The  chresard  of  the  surface  foot  was  also  low  in  the  lightly  irrigated  plat, 
but  a  good  supply  occurred  deeper.  The  fully  irrigated  crop  had  been 
watered  on  June  28,  and  here  the  plants  had  made  their  best  development. 

In  all  the  plats,  in  addition  to  12  to  14  nearly  full-grown  leaves,  each 
plant  had  3  or  4  only  partly  developed,  these  being  somewhat  more  advanced 
in  the  fully  watered  plat,  where  the  leaves  were  also  considerably  larger. 
They  were  5  inches  high  in  dry  soil  and  increased  progressively  to  12  and 
14  inches  in  the  moister  plats.  The  lateral  spread  of  tops,  which  was  9  to  12 


28 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


inches  for  the  dry-land  plants,  reached  18  inches  in  the  irrigated  plats,  those 
in  the  fully  irrigated  field  being  more  turgid  and  assuming  a  more  erect 
position  (plate  3). 

The  roots  had  made  a  most  remarkable  growth  during  the  30-day  interval, 
branching  profoundly  and  extending  well  into  or  beyond  the  third  and 
fourth  foot  of  soil  (fig.  11).  Thus,  they  had  doubled  in  length  and  increased 
the  absorbing  area  many  fold.  Differences  in  development  were  even  more 
pronounced  than  at  the  earlier  examination,  the  outstanding  features  of  the 
root  system  in  the  fully  watered  plat  being  the  marked  growth  of  the 
shallow  absorbing  system  and  the  development  of  long,  deeply  penetrating 
branches  in  the  subsoil.  The  dry-land  plants  had  neither  of  these  habits, 
but  were  characterized  by  large  numbers  of  horizontally  spreading  major 


Fig.  11. — Sugar  beets  about  3  months  old:  A,  dry  land  with  low  holard  of  subsoil; 

B,  fully  irrigated  soil,  1922. 


laterals  in  the  surface  12  to  18  inches,  where  soil  moisture  had  been  con¬ 
stantly  more  abundant.  Among  the  dry-land  plants  the  tap-roots  were 
slightly  less  than  2  inches  in  diameter,  but  in  the  fully  watered  plat  they 
were  2.5  inches.  All  tapered  so  rapidly  that  even  the  larger  ones  were 
scarcely  half  an  inch  in  width  6  inches  below  the  surface.  In  the  hard  soil 
of  the  dry  land  they  zigzagged  downward  to  depths  of  30  to  46  inches,  while 
in  moist  soil  they  pursued  a  more  even  vertical  course,  reaching  50  to  54 
inches  depth. 

Branches  in  the  surface  soil  were  very  limited  on  dry  land;  only  tiny 
rootlets  less  than  an  inch  in  length  occurred.  Their  growth  had  apparently 
been  stimulated  by  very  recent  showers  and  they  were  not  yet  clothed  with 
root-hairs.  In  striking  contrast,  the  beets  which  had  been  irrigated  about  9 


Experiments  With  Sugar  Beets. 


29 


days  earlier  had  developed  60  to  75  roots  per  linear  inch  in  zones  4  or  5 
inches  long  on  two  sides  of  the  tap-root.  They  spread  horizontally  for  dis¬ 
tances  of  3  to  5  inches  and  were  profusely  branched  with  secondary  laterals 
at  the  rate  of  8  to  12  per  inch.  This  portion  of  the  root  system,  which  had 
failed  to  develop  in  the  drier  soil,  added  materially  to  the  absorbing  area  of 
the  rapidly  developing  plants.  The  smaller  dry-land  plants  gave  off  many 
strong,  wide-spreading  laterals  in  the  surface  foot,  a  response  no  doubt  to 
the  very  low  water-content  of  the  deeper  soil.  These  became  progressively 
younger  and  shorter  downward,  but  the  number  throughout  the  course  of 
the  tap-root  was  usually  4  to  7  branches  per  inch.  The  sublaterals  were  also 
long  and  rebranched.  In  the  moist  soil,  however,  long  branches  occurred 
regularly  in  the  first,  second,  and  third  foot,  some  being  over  2  feet  long. 
The  direction  of  these  roots  away  from  the  horizontal  was  marked.  Like 
the  tap-roots,  they  were  profusely  branched  and  rebranched  with  both  long 
and  short  laterals.  The  roots  of  the  lightly  watered  beets  were  in  many 
ways  intermediate  to  those  described.  The  course  of  the  tap-root  was  some¬ 
what  irregular,  but  not  to  so  great  an  extent  as  in  the  dry  land.  The  surface 
roots  were  in  extreme  cases  an  inch  long,  but  as  a  whole  poorly  developed, 
since  water  in  the  surface  soil  was  scarce,  while  the  larger  branches  ran  off 
more  horizontally  than  in  the  more  normally  developed  fully  watered  plants. 

In  both  of  the  irrigated  plats  some  interesting  cases  of  root  stratification 
due  to  soil  structure  were  encountered.  In  one  trench,  at  a  depth  of  16 
inches,  there  occurred  a  local  stratum  of  harder  clayey  soil  a  foot  in  thick¬ 
ness.  Another  shallow  layer  similar  in  nature  was  encountered  at  3.5  feet. 
At  both  depths,  undoubtedly  due  to  the  greater  nutrient  content  in  these 
non-sandy  soils,  long,  densely  branched  roots  ran  off  horizontally  in  great 
profusion,  contrasting  in  a  striking  manner  with  the  more  poorly  branched 
parts  above  and  below.  This  local  irregularity  in  soil  structure  clearly 
shows  the  effects  of  different  partial  environments  upon  root  development. 
Similar  cases  have  been  found  among  native  plants  (cf.  Weaver,  1919  :  10). 

A  final  study  of  the  beets  was  made  on  September  12.  A  heavy  rain  (0.7 
inch)  on  July  29  and  another  (1.2  inches)  on  August  3  had  somewhat 
replenished  the  soil- water  (table  6),  although  in  the  unirrigated  plat  very 
little  water  was  available  at  any  time  (table  10) .  The  lightly  watered  plat 
was  irrigated  for  the  first  time  on  July  15  and  again  on  August  19,  the  fully 
irrigated  one  3  times,  viz,  on  June  28,  July  22,  and  August  19. 

The  plants  at  this  time  had  20  to  30  leaves  each,  those  in  dry  land  being 
only  9  inches  long,  while  in  the  irrigated  plats  they  were  twice  this  length 
and  had  three  or  four  times  as  much  photosynthetic  area,  those  in  the 
fully  watered  plats  being  the  larger.  Effects  of  drought  were  very  evident. 
Some  of  the  plants  in  the  dry  land  had  died  and  on  all  many  of  the  outer 
leaves  were  dead,  while  the  others  frequently  wilted  so  badly  that  they 
did  not  recover  even  at  night.  The  diameter  of  the  tops  of  these  drooping 
plants  was  19  inches,  as  was  also  that  of  the  lightly  watered  plants,  while 
in  the  other  plat  they  were  23  inches  in  width.  In  the  fully  irrigated  plat 
some  of  the  older  outer  leaves  were  dead  or  drying,  but  this  condition  was 
more  pronounced  in  the  lightly  watered  area. 

Root  development  was  correlated  with  that  of  tops.  The  fleshy  tap-roots 


30 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


were  3  to  6  inches  in  diameter  in  the  irrigated  soil  but  only  about  2.75 
inches  in  the  dry  land.  Moreover,  while  the  dry-land  plants  had  increased 
their  depth  from  the  third-foot  level  to  about  3.5  feet  (maximum  4.5  feet) 
since  the  last  examination,  those  in  the  irrigated  plats,  which  were  about 
4  feet  deep,  now  occupied  the  fifth  and  a  part  of  the  sixth  foot  of  soil 
(maximum  depth  6  feet).  While  the  root  plan  of  the  irrigated  plants,  with 
their  widely  spreading  horizontal  surface  system  and  rather  vertically 
descending  and  deeply  penetrating  major  branches,  was  fairly  well  blocked 


Fig.  12. — Sugar  beets  on  September  12:  A,  dry  land;  B,  fully  irrigated  soil,  1922. 

out  on  July  7  at  the  preceding  examination,  marked  changes  had  occurred 
in  the  root  habit  of  the  dry-land  plants  (fig.  12).  Here  the  two  zones 
of  surface  laterals,  which  had  then  just  appeared,  were  now  well  developed. 
At  a  depth  of  1  to  7  inches  these  arose  in  great  profusion  from  two  sides 
of  the  tap-root  and  ran  off  horizontally  for  distances  of  3  to  7  inches,  in 
response  to  the  increased  surface  moisture  due  to  rains.  Near  the  lower  edge 
of  these  zones  they  were  supplemented  by  larger  and  longer  roots  which 
spread  10  to  34  inches  and  were  rebranched  to  the  fifth  order  at  the  rate 
of  10  to  14  rootlets  per  inch,  the  whole  forming  a  close  network  in  the 
dry  soil.  On  the  larger  roots  of  the  irrigated  plants  these  lateral  root- 
producing  zones  were  longer,  as  were  also  some  of  the  smaller  roots,  but 
the  larger  ones,  originating  from  the  base,  did  not  extend  beyond  2  feet 
and  were  less  profusely  branched. 


Experiments  With  Sugar  Beets. 


31 


A  root  habit  frequently  found  in  the  harder  soils  of  dry  land,  and  also 
met  occasionally  in  the  lightly  watered  plat,  was  that  of  the  tap-root  break¬ 
ing  up  into  two  or  three  or  sometimes  more  branches  of  similar  diameter. 
This  frequently  occurred  at  depths  of  only  6  or  8  inches,  but  sometimes 
deeper.  Among  7  individuals  examined  in  the  mellow  moist  soil  of  the 
irrigated  plat,  only  1  showed  this  behavior,  and  here  it  divided  at  12  inches 
depth. 


1FT. 

\ 

fit 

( 

)  < 

A 

B 

Fig.  13. — Sugar  beet  roots  about  2  months  old: 
A,  dry  land;  B,  irrigated  soil,  1923. 


Fig.  14. — Sugar  beets  about  3  months  old:  A,  dry  land;  B,  irrigated  soil,  1923. 


32 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


Many  of  the  deeper  and  formerly  short  branches  in  the  dry  land  had 
now  reached  2  or  3  feet  in  length.  Their  course  was  almost  invariably 
rather  obliquely  downward,  in  this  respect  resembling  the  dry-land  alfalfa, 
practically  none  spreading  laterally  through  a  distance  greater  than  7 
inches.  These,  with  their  profuse  branches,  occupied  the  third  and  some¬ 
times  a  part  of  the  fourth  foot  of  soil  more  or  less  completely.  In  the 
irrigated  plants  the  roots  usually  spread  more  widely  in  the  clayey  stratum, 
in  some  instances,  to  2.5  feet. 

Seepage  water  occurred  late  in  the  season  at  about  5  feet  depth  in  the 
fully  irrigated  plats,  and  the  root  penetration  was  not  so  great  as  in  the 
lightly  watered  one,  probably  because  of  deficient  aeration.  Branching 
was  similar  in  the  two  plats,  except  for  a  greater  tendency  for  a  wider 
lateral  spread  of  roots  in  the  shallower  soil  of  the  drier  land.  The  sub¬ 
laterals  were  longer,  sometimes  reaching  25  inches,  while  none  were  found 
to  exceed  8  inches  in  the  more  moist  soil.  The  surface  root  system  of 
the  fully  watered  plants  contained  a  greater  number  of  roots  in  the  furrow 
slice,  but  they  were  hardly  as  long  as  in  the  drier  soil  of  the  lightly  irrigated 
plats. 

The  beets  in  the  dry-land  plat  yielded  at  the  rate  of  only  2.5  tons  per 
acre,  those  in  the  lightly  watered  plats  21  tons,  while  the  fully  watered 
plats  yielded  22.5  tons  per  acre.  They  were  harvested  on  September  26. 


33 


Experiments  With  Potatoes. 


EXPERIMENTS  WITH  POTATOES. 

Bliss's  Triumph  potatoes,  widely  grown  in  the  region  as  an  early  variety, 
were  planted  in  the  three  plats  on  May  6.  Large  pieces  of  tubers  of  uniform 
size  were  placed  at  14-inch  intervals  in  furrows  3  feet  apart  and  covered 
to  a  depth  of  3  or  4  inches.  By  frequent  shallow  tillage  the  plats  were 
not  only  kept  free  from  weeds,  but  also  a  good  soil  mulch  was  maintained 
in  the  dry  land. 

The  first  examination  of  the  root  habit  was  made  on  June  21-23.  The 
May  rainfall  (1.3  inches)  fell  from  the  27th  to  31st,  while  the  0.25  inch 
in  June  added  nothing  to  the  water-content  of  the  soil.  Table  6  shows 


Table  11. — Holard  of  potato  plats  in  excess  of  hygroscopic  coefficient,  1922. 


Date,  etc. 

0  to  0.5 
foot. 

0.5  to  1 
foot. 

1  to  2 
feet. 

2  to  3 
feet. 

3  to  4 
feet. 

Dry  land: 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

May  8 . 

3.8 

3.5 

3.9 

-1.0 

3.8 

29 . 

2.7 

3.4 

2.6 

-1.5 

0.0 

June  17 . 

0.8 

3.0 

4.0 

1.1 

0.0 

23 . 

0.0 

0.8 

3.8 

July  5 . 

1.8 

3.9 

3.1 

Hygro.  coef . 

4.2 

5.4 

4.4 

4.3 

5.6 

Lightly  irrigated: 

May  8 . 

5.3 

8.9 

13.1 

10.0 

6.0 

29 . 

6.6 

8.8 

11.7 

12.8 

5.6 

June  23 . 

2.1 

4.4 

9.2 

10.6 

28 . 

3.8 

3.6 

13.1 

11 .4 

28 . 

(14.5) 

(14.5) 

(7.3) 

(5.4) 

July  5 . 

5.0 

6.6 

9.0 

10.3 

15 . 

4.5 

4.3 

13.0 

12.8 

15 . 

(8.0) 

(8.0) 

(2.9) 

(2.1) 

22 . 

7.2 

7.0 

14.4 

13.6 

22 . 

(4.9) 

(4.7) 

(2.4) 

(0.0) 

Hygro.  coef. ....... 

2.9 

3.1 

3.0 

5.0 

4.1 

Fully  irrigated: 

May  8 . 

5.0 

9.0 

13.5 

10.4 

5.9 

29 . 

6.2 

8.4 

11.3 

12.9 

5.8 

June  23 . 

2.5 

4.4 

7.4 

11.5 

23 . 

(10.8) 

(10.8) 

(5  7) 

(2.4) 

28 . 

8.6 

8  3 

12.6 

8  1 

28 . 

(9.0) 

(9.2) 

(6  2) 

(4.8) 

July  5 . 

8.9 

8.6 

11  5 

10  9 

5 . 

(5.0) 

(5.2) 

(2  6) 

(0.0) 

15 . 

5.2 

4.9 

9.7 

9.3 

15 . 

(6.0) 

(6.2) 

(4.9) 

(1.2) 

22 . 

10.9 

10.6 

7.6 

10.8 

22 . 

(4.4) 

(4.4) 

(6.9) 

(0.7) 

Aug.  3 . 

5.0 

4.7 

9.9 

10.8 

3 . 

(6.2) 

(6.3) 

(1.7) 

(0.8) 

Hygro.  coef . 

4.6 

4.9 

8.0 

6.8 

4.0 

that  no  water  was  available  in  the  third  foot  and  only  a  small  amount  in 
the  surface  soil.  Although  neither  of  the  irrigated  plats  had  been  watered, 
enough  moisture  was  present  to  promote  good  growth.  Two  to  four  stalks 
occurred  in  a  hill,  and  the  plants  were  8  to  11  inches  tall,  being  slightly 
smaller  in  the  dry-land  plats. 

The  profound  differences  in  the  extent  and  branching  of  the  roots  in  the 
two  plats  are  shown  in  figure  15,  a,  b.  In  all  the  plats  50  to  85  roots  per 


34 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


plant  originated  either  about  the  old  tuber  or  from  the  nodes  above.  Many 
of  these  in  dry  land  extended  horizontally  throughout  their  whole  length, 
penetrating  the  surface  soil  and  ending  at  depths  of  only  1  to  8  inches. 
Others,  after  extending  outward  for  12  to  18  inches,  gradually  turned 
downward  and  ended  at  depths  of  1  to  1.5  feet;  usually  3  to  5  would 
take  a  rather  vertically  downward  course,  some  reaching  the  23-inch  level. 
All  were  supplied  with  laterals  as  thickly  as  15  to  20  per  inch,  of  which 
the  longest  were  18  inches,  although  the  average  scarcely  exceeded  5  inches. 
These  were  very  thickly  rebranched  to  near  their  tips.  Thus,  the  surface 
foot  of  soil,  beginning  just  beneath  the  dust  mulch,  was  filled  with  an 
absorbing  net-work  of  white,  succulent,  tender  roots,  while  the  second  foot 
was  beginning  to  be  exploited  to  satisfy  the  heavy  demands  for  water. 
Root  habit  in  the  two  irrigated  plats  was  at  this  time  identical  and  differed 
from  that  in  the  dry  land  in  a  slightly  smaller  penetration,  fewer  roots 
occurring  in  the  second  foot  of  soil,  and  especially  in  fewer  and  shorter 
branches.  For  example,  the  maximum  lateral  spread  seldom  exceeded 
20  inches  and  was  usually  much  less  as  compared  to  the  usual  spread  in 
the  dry  land  of  18  inches,  with  a  maximum  exceeding  2.5  feet.  Clearly, 
the  scarcity  of  water  in  the  dry  land  had  resulted  in  an  extraordinary  root 
growth.  Young  tubers  only  2  or  3  mm.  in  diameter  had  begun  to  appear 
in  great  numbers  on  all  of  the  plants. 

Owing  to  hot,  dry  weather,  coupled  with  a  very  low  chresard,  which  at 
certain  levels  was  practically  nil,  the  crop  in  the  dry  land  had  not  increased 
in  height  by  July  7,  when  again  examined.  The  plants  wilted  almost  daily 
and  regained  partial  turgidity  only  during  the  cool  nights.  Under  these 
conditions  growth  was  poor.  The  crop,  which  had  been  irrigated  on  June  28, 
was  18  inches  tall,  of  a  healthy  dark-green  color,  and  was  growing  rapidly, 
a  few  blossoms  having  appeared  (June  11).  Where  water  had  been  provided 
at  two  intervals  (June  23  and  June  28),  the  plants  were  2  inches  taller, 
growing  luxuriantly,  and  coming  well  into  blossom  (plate  4).  Correlating 
with  this  excellent  above-ground  development,  the  roots  had  grown  propor¬ 
tionately.  But  just  as  little  change  had  occurred  in  the  tops  in  the  dry 
land;  so,  too,  the  roots  had  developed  scarcely  beyond  the  stage  reached 
two  weeks  earlier.  In  fact,  the  lateral  spread  and  branching  had  not 
changed,  except  that  the  branches  now  extended  to  the  very  root-tips, 
indicating  the  cessation  of  root  elongation.  However,  the  working  depth 
had  been  increased  about  6  inches  and  the  maximum  penetration  to  26 
inches.  None  penetrated  into  the  hardpan  at  26  inches  depth.  Shortage 
of  water  had  caused  a  cessation  of  development,  and  in  spite  of  the  wonder¬ 
fully  extensive  root  system,  the  plants  were  losing  ground.  The  tubers 
had  developed  scarcely  at  all.  Only  a  very  few  were  6  mm.  in  diameter, 
rarely  as  large  as  15  mm. 

The  fully  watered  potatoes  had  increased  their  absorbing  area  by  extend¬ 
ing  their  roots  both  outward  and  downward  (cf.  fig.  15,  a  and  b),  thus 
keeping  pace  with  the  growth  of  the  tops.  The  lateral  spread  had  now 
reached  a  maximum  of  2  feet  on  all  sides  of  the  plant.  Although  the  great 
bulk  of  the  roots  occurred  in  the  surface  foot,  they  were  not  infrequently 
deeper,  a  few  having  penetrated  an  inch  into  the  third  foot  of  soil. 


‘iSftrmmr  OF  ILLINOIS  LIBRARY 


Fig.  15. — One-half  of  the  root  system  of  potatoes  when  6  weeks  old: 


A,  dry  land;  B,  irrigated  soil.  And  about  9  weeks  old; 
E,  mature  plants,  dry  land,  1923. 


C,  lightly  watered,  and  D,  fully  irrigated  soil,  1922; 


Experiments  With  Potatoes. 


35 


Root  habit  in  the  lightly  watered  area  differed  not  only  in  lateral  extent 
and  depth  of  penetration,  but  also  in  more  profuse  branching.  Surface 
roots  were  sometimes  4  inches  longer  in  this  drier  soil,  while  more  roots 
were  found  that  took  a  vertical  or  nearly  vertical  course  downward. 
Thus  the  second  foot  of  soil  became  much  more  thoroughly  occupied,  the 
working  depth  reaching  2  feet  as  compared  with  16  inches  in  the  wetter 
soil;  the  maximum  penetration  likewise  was  7  inches  deeper  (fig.  15,  c). 

As  regards  branching,  12  to  20  smaller  laterals  regularly  occurred  per 
inch,  as  against  9  to  16  in  the  fully  irrigated  soil,  but  the  branches  in  the 
two  cases  were  very  similar  in  length.  Moreover,  the  main  roots  showed 
a  much  greater  tendency  to  break  up  into  3  or  4  long  branches  in  the 
drier  soil.  Tubers  were  abundant  in  both  plats,  being  larger  (6  to  33  mm. 
in  diameter)  in  the  fully  irrigated  one.  Moreover,  the  rhizomes  upon 
which  they  were  borne  were  longer  (sometimes  15  inches  in  extent)  than 
those  growing  in  the  harder,  drier  soil.  Thus,  root  development  in  the 
three  fields  was  distinctly  different,  the  differences  being  readily  correlated 
with  differences  in  the  available  water-supply.  The  yield  at  maturity  in 
the  dry  land  was  at  the  rate  of  19  bushels  per  acre,  all  the  tubers  being 
small,  in  the  fully  watered  plats  160  bushels,  while  in  the  lightly  watered 
plat  303  bushels  per  acre  were  grown. 


36 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


EXPERIMENTS  WITH  CORN. 

A  yellow  dent  corn,  Minnesota  No.  13,  a  variety  considered  the  best 
adapted  for  this  region,  was  planted  in  the  three  plats  on  May  10.  Shallow 
furrows,  3  feet  apart,  were  made  with  a  plow  and  the  kernels  dropped 
into  these  16  inches  apart  and  covered  to  a  depth  of  3  inches.  In  all  the 
plats  the  crop  was  given  shallow  cultivation  from  time  to  time  in  order 
to  prevent  the  growth  of  weeds  and  also  to  furnish  a  mulch  in  the  dry 
land.  Sufficient  moisture  was  present  even  in  the  latter  to  cause  good 
germination  and  early  growth  (table  12). 


Table  12. — Holard  of  corn  plats  in  excess  of  hygroscopic  coefficients,  1922. 


Date,  etc. 

0  to  0.5 
foot. 

0.5  to  1 
foot. 

1  to  2 
feet. 

2  to  3 
feet. 

3  to  4 
feet. 

Dry  land: 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

May  17 . 

June  22 . 

5.8 

4.2 

5.0 

5.7 

2.9 

7.3 

0.0 

0.2 

July  5 . 

0.0 

2.0 

4.5 

2.7 

Sept.  12 . 

0.1 

1.7 

4.1 

1.9 

3.7 

Hygro.  coef . 

4.2 

5.4 

4.4 

4.3 

6.6 

Lightly  irrigated: 

May  17 . 

4.9 

8.4 

13.2 

9.0 

8.0 

17 . 

(9.0) 

(9.0) 

(0.8) 

(3.3) 

June  22 . 

2.0 

6.8 

14.2 

14.8 

July  5 . 

1.6 

1.4 

6.9 

9.7 

5 . 

(11-0) 

(11.7) 

(7.3) 

(5.7) 

Sept.  12 . 

0.0 

2.1 

2.8 

8.6 

10.5 

Hygro.  coef . 

2.9 

3.1 

3.0 

5.0 

4.1 

Fully  irrigated: 

May  17 . 

4.7 

8.5 

13.0 

9.2 

7.9 

17 . 

(8.8) 

(9.2) 

(0.9) 

(3.4) 

June  22 . 

0.2 

3.4 

8.6 

12.8 

22 . 

(17.0) 

(17.1) 

(7.7) 

(0.0) 

July  15 . 

4.0 

1.4 

7.6 

3.0 

15 . 

(7.0) 

(7.2) 

(1.6) 

(5.4) 

Aug.  3. . . . 

3.2 

5.8 

5.2 

9.3 

3 . 

(6.3) 

(6.0) 

(4.6) 

(3.5) 

19 . 

6.9 

4.3 

9.5 

5.7 

19 . 

(5.8) 

(6.0) 

(1.0) 

(3.1) 

Sept.  12 . 

3.7 

12.9 

10.5 

10.7 

9.0 

Hygro.  coef . 

* 

5.5 

8.1 

8.0 

4.5 

2.3 

The  first  examination  of  root  habit  and  development  was  made  on 
June  21-23,  when  the  plants  were  about  6  weeks  old.  In  the  dry  land 
and  lightly  watered  plat  (which  had  been  irrigated  a  week  after  planting) 
the  plants  had  7  or  8  leaves  each  and  were  12  to  15  inches  tall,  those  in 
dry  land  being  about  2  inches  the  higher.  Like  those  in  the  other  plat, 
which  had  also  been  irrigated  on  May  17,  they  were  making  a  good  growth. 
The  latter,  however,  were  only  10  to  14  inches  tall  and  had  but  5  or  6 
leaves. 

The  general  root  habit  of  corn  at  this  age,  as  well  as  the  differences  in 
habit,  is  clearly  shown  in  figure  16.  Even  a  glance  reveals  marked  differ¬ 
ences  in  the  several  plats.  Each  plant  was  furnished  with  10  to  16  thick, 
fibrous  roots.  In  the  dry  land,  while  some  ran  off  rather  horizontally, 
most  of  them  grew  outward  and  downward  1  or  2  feet;  the  longest  extended 


Experiments  With  Corn. 


37 


to  2.5  feet,  when  it  turned  downward  into  the  second  foot  of  soil.  In  fact, 
this  latter  tendency  was  marked,  the  roots  seeming  to  seek  moister  soil. 
The  longest  penetrated  a  little  into  the  third  foot;  a  few  younger  and 
shorter  roots  ran  rather  straight  downward  and  branching  throughout  was 
profuse. 


Fig.  16. — Root  system  of  6- weeks-old  corn:  A,  dry  land;  B,  lightly  irrigated; 

C,  fully  irrigated  soil. 

In  the  fully  watered  plat  the  roots  ran  much  more  horizontally,  spreading 
even  2  or  3  feet  at  a  depth  of  only  6  to  10  inches.  Vertically  penetrating 
roots  were  practically  absent,  and  only  a  few  entered  the  second  foot  of 
soil.  In  fact,  the  bulk  of  the  root  system  was  in  the  first  6  inches.  This 
normal  surface-rooting  habit  (cf.  Weaver,  Jean,  and  Crist,  1922  :  21)  is 
in  marked  contrast  to  that  of  dry  land.  Moreover,  great  differences  were 
found  in  the  degree  of  branching.  While  in  the  watered  plat  the  laterals 


38 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


averaged  12  per  inch,  they  occurred  at  the  rate  of  20  to  35  per  inch  in 
dry  land.  Here  they  averaged  4  inches  in  length  and  were  rebranched 


Fig.  17. — Corn  about  8  weeks  old:  A,  dry  land;  B,  lightly  irrigated; 

C,  fully  irrigated  soil. 

at  the  rate  of  18  per  inch,  while  in  the  moist  soil  the  average  scarcely 
exceeded  2  inches  and  only  9  branchlets  per  inch  occurred. 


Experiments  With  Corn. 


39 


Conditions  in  the  lightly  irrigated  plat  were  intermediate,  an  effect 
brought  about  by  differences  in  soil,  the  water-content  being  much  the 
same  as  in  the  fully  irrigated  one.  In  the  latter,  a  heavier  subsoil  underlay 
the  furrow  slice  of  sandy  loam,  while  in  the  lightly  irrigated  plat  the 
sandy  loam  extended  beyond  the  second  foot.  Here  the  widely  spreading, 
shallow,  horizontal  roots  were  fewer  and  shorter,  a  pronounced  tendency 
to  run  off  obliquely  and  especially  to  turn  vertically  downward  being 
manifest.  Many  entered  well  into  the  second  foot  of  soil  and  some  reached 
depths  of  27  inches.  A  good  growth  of  younger,  vertically  descending 
roots,  quite  absent  in  the  other  watered  plat,  was  probably  a  response  to 
the  dry,  hot  weather  of  the  10  days  preceding,  which  caused  the  leaves 
to  curl  in  the  afternoons.  The  branching  closely  resembled  that  in  the 
other  watered  plat,  but  was  slightly  greater. 

The  next  examination  was  made  over  2  weeks  later,  on  July  8-10.  No 
efficient  rain  had  fallen  and  no  water  was  available  in  the  surface  6  inches 
of  the  dry  land,  while  only  2  to  4  per  cent  remained  in  the  deeper  soil 
(table  12).  The  lightly  irrigated  soil  was  also  very  dry  until  it  was 
watered  on  July  5,  but  the  other  plat  had  been  irrigated  a  second  time 
on  June  22.  The  crop  in  the  fully  watered  plat  was  34  inches  high,  37 
inches  in  the  lightly  watered  soil,  but  only  24  in  dry  land.  In  all  three 
fields  the  tassels  were  just  beginning  to  appear.  The  crop  was  in  a  flour¬ 
ishing  condition,  except  in  the  dry  land,  where  it  showed  the  effects  of 
the  marked  drought.  The  leaves  were  tightly  rolled  during  the  hottest 
part  of  the  day  and  sufficient  water  was  not  available  for  them  to  recover 
even  during  the  cool  nights  (plate  5). 

In  response  to  the  low  water-content,  the  roots  had  made  a  more  marked 
growth  in  the  dry  land  than  in  either  of  the  other  plats  (fig.  17).  The 
lateral  spread,  especially  of  the  shallower  roots,  had  been  greatly  increased, 
reaching  a  maximum  of  42  inches,  furnishing  water  from  an  area  hitherto 
unoccupied.  New  roots  had  been  added  in  such  abundance  that  a  total 
of  33  to  45  was  found  on  each  plant,  as  in  the  other  plats.  These  added 
greatly  to  the  occupation  of  the  first  and  second  feet  of  soil,  while  the 
older  roots  had  extended  their  area  far  into  the  third  and  fourth  feet.  An 
average  depth  of  30  inches  was  determined  and  a  maximum  penetration 
of  46  inches.  Long,  profusely  rebranched  laterals  were  exceedingly  abun¬ 
dant.  These,  like  the  larger  roots,  were  often  tortuous  in  their  course 
because  of  the  difficulty  in  penetrating  the  hard,  dry  soil.  Growth  was 
still  occurring,  as  was  shown  by  the  presence  of  new  main  roots  only  a  few 
inches  long. 

Thus,  while  the  dry-land  corn  was  deeply  rooted,  that  in  the  fully  irri¬ 
gated  field,  with  stalks  a  foot  taller,  was  largely  confined  to  the  surface 
foot  of  soil,  where  moisture  was  rather  constantly  abundant.  The  lateral 
spread  of  roots  was  much  less  than  in  dry  land,  but  more  of  the  roots  ended 
in  the  surface  foot.  The  working  level  was  only  2  feet  deep  and  the 
maximum  penetration  4  inches  greater.  Branching,  as  at  the  preceding 
examination,  was  much  less  pronounced  and  the  laterals  were  much  shorter. 

Root  systems  in  the  lightly  watered,  more  sandy  soil  differed  from  those 
last  described  in  three  well-defined  ways.  The  first  was  the  shortness 
of  the  newer  roots  in  the  surface  soil,  most  of  which  had  evidently  grown 


40 


Root  Behavior  and  Crop  Yield  Under  Irrigation 


Fig.  18. — Dry-land  corn  on  September  12. 


^  / 

■ 

§i 

$ 

il 

» 

If 

i] 

m 

il 

P 

f 

1 

4 

13 

1 

■ 

5 

T  i 

i:  j9 

1 

6 

1 

i{ 

. 

Fig.  19. — Corn  in  fully  irrigated  soil,  September  13 


Experiments  With  Corn. 


41 


since  the  plat  was  irrigated  only  5  days  earlier.  They  were  only  1  to  5 
inches  long,  densely  covered  with  root-hairs,  but  entirely  unbranched. 
Absorption  in  the  surface  soil  was  much  more  poorly  provided  for  than 
in  the  more  moist  plat,  where  the  lateral  spread  of  roots  was  also  greater. 
A  second  difference  was  the  great  depths  to  which  the  older  roots  had 
penetrated.  A  working-level  of  33  inches  had  been  attained  (exceeding 
that  in  dry  land,  where  the  deeper  soil  was  without  available  water)  and 
a  maximum  depth  of  52  inches.  Finally  a  great  increase  in  branching 
(especially  in  length  of  laterals)  had  occurred  when  compared  either  with 
its  earlier  development  or  with  that  in  the  fully  irrigated  plat.  During 
the  week  preceding  irrigation  the  soil  was  so  dry  that  the  corn  showed  a 
marked  rolling  of  its  leaves,  and  it  was  probably  in  response  to  this  con¬ 
dition  that,  as  in  the  dry  land,  the  growth  of  the  branches  occurred. 

A  final  study  of  root  habits  of  corn  was  made  on  September  12  and  13. 
Aside  from  a  heavy  rain  (0.7  inch)  on  July  29  and  another  (1.2  inches) 
on  August  3,  no  efficient  moisture  fell  during  the  interval  since  the  last 
examination.  Thus,  drought  conditions  prevailed  in  the  dry  land,  although 
at  the  time  of  root  excavation  some  available  moisture  remained  in  the 
second  foot  of  soil,  the  corn  having  “fired”  and  lost  most  of  its  leaves 
during  July,  thus  greatly  reducing  transpiration.  The  lightly  watered  plat 
had  not  been  irrigated  since  July  5,  and  table  12  shows  that  the  first  2  feet 
of  soil  were  very  dry.  Water  had  been  added  to  the  other  plat  on  July  15 
and  on  August  3  and  19,  and  hence  an  excellent  holard  was  maintained. 
In  the  dry  land  the  crop  showed  little  growth,  having  reached  a  height  of 
only  3.5  feet,  so  extreme  was  the  drought.  The  plants  in  the  irrigated  plats 
were  rather  uniformly  7  feet  high  and  were  furnished  with  large,  well-filled 
ears.  The  leaves  were  dry  and  the  husks  were  almost  dry,  while  the  kernels 
of  corn  were  well  dented  and  nearly  dry.  These  conditions  were  somewhat 
more  pronounced  in  the  lightly  irrigated  field. 

Practically  no  change  had  occurred  in  the  root  habit  in  the  dry  land 
(fig.  18).  The  occupation  of  the  soil  in  the  zone  directly  below  the  plant 
was  somewhat  more  thorough  and  branches  now  occurred  on  all  the  roots 
to  their  very  tips.  The  plants  were  unable  to  furnish  sufficient  water  to 
keep  the  leaves  turgid,  and  these  in  turn  failed  to  supply  the  needed  mate¬ 
rials  for  further  root  growth.  But  in  the  fully  irrigated  plat  marked 
changes  had  occurred  (fig.  19).  The  roots,  formerly  confined  to  the  first 
foot  or  two  of  soil,  now  extended  into  the  fifth  and  sixth  foot,  while  many 
of  the  horizontal  laterals  had  likewise  turned  downward  and  penetrated 
deeply.  The  deepest  roots,  however,  were  the  rather  vertically  descending 
ones  of  later  origin.  A  working  depth  of  40  inches  and  a  maximum  pene¬ 
tration  of  70  inches  were  found.  Seepage  water  was  encountered  at  the 
6-foot  level. 

This  remarkable  root  system  was  surpassed,  however,  by  that  which 
developed  in  the  drier,  somewhat  sandier  soil  in  the  lightly  irrigated  plats 
(fig.  20).  As  in  the  former  case,  50  to  70  major  roots  occurred.  Also,  the 
general  form  of  the  root  system  was  similar  to  that  just  described,  but 
some  outstanding  differences  were  found.  The  number  of  fine  surface 
roots  within  the  first  15  inches  of  soil  was  markedly  fewer,  due  no  doubt 


42 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


to  the  much  drier  soil.  The  lateral  spread  of  the  main  roots  was  also 
slightly  less,  but  the  depth  of  penetration  was  greater.  The  roots,  which 
were  just  well  started  on  July  7,  had  now  reached  a  working-level  in  the 
fifth  foot,  many  penetrating  far  beyond,  and,  with  the  downward  growth 
of  the  older,  widely  spreading  ones,  thoroughly  occupied  the  third,  fourth, 
and  much  of  the  fifth  foot  of  soil.  The  working-level  and  maximum  pene- 


Fig.  20. — Corn  in  lightly  irrigated  soil,  September  13. 


tration  were  58  and  80  inches  respectively,  as  compared  with  40  and  70 
inches  in  the  plat  more  freely  watered.  Even  greater  depths  might  have 
been  attained  except  for  the  presence  of  seepage  water  at  73  inches.  More¬ 
over,  branching  was  much  more  profuse  throughout.  For  example,  in 
the  wetter  soil,  branches  of  the  first  order  ranged  from  12  to  20  per  inch, 
while  they  were  18  to  25  per  inch  in  the  drier  soil.  Also,  below  the  15-inch 


Experiments  With  Corn. 


43 


level,  the  branches  averaged  nearly  2  inches  longer  and  they  were  more 
thoroughly  rebranched.  The  root  system  as  a  whole  was  very  impressive 
and  well  fitted  to  supply  the  275  pounds  of  water  normally  needed  to 
mature  a  corn  plant  (cf.  Kiesselbach,  1916).  Thus,  with  crop  plants,  as 
with  native  species,  too  dry  soil  retards  root  growth,  but  a  fairly  moist, 
deep  one  permits  maximum  development,  the  roots  becoming  less  extensive 
in  soils  supplied  constantly  with  an  abundance  of  water.  The  plants  with 
the  best  root  systems  gave  the  greatest  yield,  the  rate  being  115  bushels  per 
acre.  The  fully  watered  plats  yielded  102  bushels  and  the  dry  land  25, 
the  quality  in  the  latter  being  very  poor. 


44 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


ENVIRONMENTAL  CONDITIONS,  1923. 


The  season  of  1923  had  an  abnormally  high  rainfall,  an  excess  of  1.4 
inches  falling  in  March  and  3.2  in  June,  that  for  April  and  May  totaling 
only  1.3  inches  below  normal  (table  8).  Moreover,  the  showers  were 
heavier  than  usual  and  quite  well  distributed,  thus  promoting  a  good 
crop  growth  even  on  the  dry  land,  especially  until  midsummer. 


Fig.  21. — Average  day  air-temperatures  (upper  lines)  and  average  night  air- 
temperatures  (lower  lines)  in  dry-land  (solid  lines)  and  irrigated  plats 
(broken  lines),  1923. 

Spring  was  2  or  3  weeks  later  than  usual.  The  average  daily  air-tem¬ 
perature,  which  was  very  similar  in  the  two  experimental  areas  throughout 
the  season,  was  11.8°  F.  lower  than  the  preceding  May,  and  3.9°  F.  lower 
for  June,  and  in  general  lower  throughout  the  summer  than  in  1922  (cf. 
figs.  2  and  21).  The  extreme  differences  between  day  and  night  tempera- 


Table  13. — Soil  temperatures  in  the  dry-land  and  irrigated  plats,  1923. 


Date. 

Depth,  2  feet. 

Depth,  3  feet. 

Depth,  4  feet. 

Dry  land. 

Irrigated. 

Dry  land. 

Irrigated. 

Dry  land. 

Irrigated. 

• 

°C. 

°  C. 

0  C. 

°  C. 

°  C. 

°  C. 

Apr.  16 . 

9.0 

8.0 

10.0 

7.5 

8.5 

7.0 

23 . 

8.0 

8.0 

11.0 

9.0 

11.0 

9.0 

30 . 

10.0 

11.0 

9.5 

9.0 

9.0 

9.0 

May  7 . 

12.5 

12.5 

11.5 

11.5 

10.5 

10.0 

14 . 

12.0 

12.0 

11.5 

11.5 

11.0 

11.0 

21 . 

14.0 

14.0 

13.0 

13.0 

12.0 

12.0 

28 . 

15.0 

15.5 

14.0 

14.0 

12.5 

13.0 

June  4 . 

18.5 

17.0 

17.0 

16.5 

16.0 

15.5 

11 . 

16.0 

16.0 

16.0 

16.0 

16.0 

15.5 

18 . 

19.0 

17.5 

17.5 

16.5 

17.5 

15.5 

25 . 

21.5 

21.0 

19.0 

18.0 

17.0 

17.0 

July  2 . 

22.0 

22.5 

20.0 

21.0 

19.0 

20.5 

9 . 

24.5 

23.0 

22.5 

22.0 

20.0 

20.5 

23 . 

24.5 

24.5 

22.5 

22.5 

21.0 

21.0 

Environmental  Conditions ,  1923 . 


45 


tures  were  again  marked.  While  the  mid-afternoon  temperatures  often 
reached  95°  to  100°  F.,  they  frequently  fell  towards  morning  to  55°  or  60°  F. 
Differences  in  soil  temperatures  were  no  more  in  evidence  than  during  1922 


May  June  July  August  Sept 


Fig.  22. — Average  day  humidity  (lower  lines)  and  average  night  humidity 
(upper  lines)  in  the  dry-land  plat  (solid  lines)  and  in  the  irrigated 
plats  (broken  lines),  1923. 


r 

May  June  ‘July  August  Sept 


Fig.  23. — Average  daily  evaporation  in  dry-land  (solid  line)  and  irrigated  plats 

(broken  line),  1923. 


46 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


(fig.  24).  A  comparison  with  the  data  of  1922  (fig.  4)  shows  that  owing 
to  cold  rains  and  snow  they  were  much  lower  during  April  and  May,  the 
temperatures  not  increasing  consistently  until  after  the  third  week  in 
May.  At  depths  of  2  to  4  feet  the  temperatures  were  not  only  quite  alike 
in  the  two  plats,  but  similar  to  those  of  the  preceding  season  (table  13). 

The  average  day  and  night  humidity  at  the  two  stations  is  shown  in 
figure  22.  No  difference  in  the  dryness  of  the  air  at  the  two  stations  is 
apparent.  A  comparison  of  the  average  day  and  night  humidity  at  the 
dry-land  station  shows  that  it  is  nearly  always  much  higher  than  during 
1922  (table  4  and  fig.  22).  The  average  daily  evaporation  at  the  two 
stations  is  also  almost  identical  (fig.  23).  Compared  with  that  of  1922, 
for  example  (fig.  3),  the  evaporation  for  May  at  the  dry-land  station  was 
only  45  per  cent  as  great,  for  June  71  per  cent,  for  July  80  per  cent,  and 
70  per  cent  as  great  for  August. 


April  May  June  Juty 

16  23  30  7  14  21  28  4  11  18  25  2  9  16  23 


Fig.  24. — Soil  temperature  in  dry-land  (solid  lines)  and  irri¬ 
gated  plats  (broken  lines)  at  depths  of  3  inches  (light 
upper  lines),  6  inches  (heavy  lines),  and  12  inches  (lower 
light  lines),  1923. 

Summarizing,  the  growing-season  of  1923,  which  opened  late,  had  a 
great  excess  of  rainfall,  lower  temperatures  than  in  1922,  especially  in  the 
earlier  part  of  the  season,  a  higher  humidity,  and  less  evaporation.  The 
air  factors  in  the  two  cropped  areas,  which  were  only  slightly  different 
the  preceding  season,  were  this  year  almost  identical.  Consequently,  differ¬ 
ences  in  root  development  may  be  attributed  almost  solely  to  soil  factors. 

The  dry-land  crops  in  1923  were  grown  in  the  same  field  as  before,  but 
in  a  portion  that  had  been  summer-fallowed  the  preceding  year  and  thus 
kept  free  from  weeds.  This  and  the  irrigated  fields  were  plowed  about  8 
inches  deep  and  repeatedly  harrowed  on  April  9,  the  spring  being  about  3 
weeks  later  than  usual  and  the  soil  too  wet  for  earlier  cultivation.  All  of 
the  irrigated  plats,  however,  had  been  previously  fertilized  with  barnyard 
manure  at  the  rate  of  5  tons  per  acre.  The  wheat  was  again  drilled  2  inches 
deep  in  rows  8  inches  apart  at  the  rate  of  90  pounds  per  acre.  This  was 
done  on  April  10,  the  crop  in  the  lightly  watered  plats  following  potatoes, 


Environmental  Conditions,  1923 . 


47 


and  that  in  the  fully  irrigated  one  following  corn.  This  selection  of  plats 
was  made  so  as  to  have  the  soil  in  any  two  as  nearly  alike  as  possible  for 
the  same  crop.  The  beets  were  drilled  an  inch  deep  in  rows  18  inches  apart 
on  April  16.  Onions  had  been  grown  the  preceding  year  in  the  beet  plats. 
On  May  30  the  crop  was  thinned  to  a  single  plant  per  foot  in  the  row. 
Both  corn  and  potatoes  were  planted  on  May  12,  the  rows  being  3  feet 
apart.  The  corn,  which  followed  beets  in  the  lightly  watered  plats  and 
summer-fallow  in  the  heavily  watered,  was  planted  2  inches  deep  and  the 
kernels  16  inches  apart  in  the  row.  The  potatoes,  which  followed  wheat 
and  onions  respectively  in  the  lightly  and  heavily  irrigated  plats,  were  cut 
into  large  pieces  which  were  planted  14  inches  apart  and  3  inches  deep. 
Shallow  tillage,  so  as  not  to  disturb  the  root  systems,  was  again  used  from 
time  to  time  as  in  1922  in  the  plats  of  corn,  beets,  and  potatoes. 

A  very  severe  hail  occurred  on  June  14;  damage  to  the  irrigated  crops 
being  much  greater  than  to  those  in  the  dry  land.  In  the  former,  alfalfa 
was  entirely  defoliated  and  the  stems  bruised  or  broken,  but  that  in  the 
dry  land  was  only  slightly  harmed.  Similarly,  the  dry-land  wheat  was 
scarcely  affected,  but  that  in  the  other  plats  was  so  badly  damaged  that 
only  about  10  per  cent  headed,  the  original  crop  being  largely  replaced 
by  one  derived  from  the  tillers  sprouting  from  the  base  of  the  plants. 
Potatoes  in  the  irrigated  plats  were  entirely  defoliated  and  some  of  the 
stems  broken.  The  corn,  which  at  this  time  was  about  a  foot  high,  was  also 
badly  damaged.  Immediately  after  the  hail,  about  half  of  the  corn  was 
replanted,  so  that  normal  field  conditions  were  maintained  as  to  competition. 
The  sugar  beets  at  the  time  of  the  storm  had  8  or  10  leaves  each,  but  of 
these  only  remnants  were  left.  Owing,  however,  to  very  favorable  weather 
and  the  previous  vigorous  growth,  all  of  the  crops  (except  potatoes) 
recovered  rapidly  in  a  most  remarkable  manner. 

On  May  17  soil  samples  were  secured  from  all  the  plats  for  purposes  of 
nitrogen  determination  (table  14).  Determinations  were  made  with  the 
phenoldisulphonic-acid  method,  nitrogen  in  the  form  of  N03,  with  whatever 
combined,  being  ascertained. 


Table  14. — Nitrogen-content  of  soil  in  the  several  plats ,  May  17,  1923,  in  terms  of  p.  p.  m.  of 

nitric  nitrogen. 


Plat. 

0  to  0.5 
foot. 

0.5  to  1 
foot. 

1  to  2 
feet. 

Plat. 

0  to  0.5 
foot. 

0.5  to  1 
foot. 

1  to  2 
feet. 

Alfalfa: 

Potatoes : 

Dry  land . 

None 

None 

None 

Dry  land . 

2.3 

5.3 

7.0 

Irrigated . 

1.4 

Trace 

None 

Lightly  irri- 

Wheat : 

gated . 

10.9 

9.9 

10.0 

Dry  land . 

4.2 

5.2 

8.1 

Fully  irrigated . 

5.9 

10.7 

7.1 

Lightly  irri- 

Corn: 

gated . 

4.1 

8.5 

10.3 

Dry  land . 

4.0 

5.1 

8.7 

Fully  irrigated. 

2.8 

3.8 

2.6 

Lightly  irri- 

Beets: 

gated . 

7.5 

5.7 

2.8 

Dry  land . 

4.1 

8.8 

8.8 

Fully  irrigated . 

4.7 

6.2 

5.1 

Lightly  irri- 

gated . 

5.6 

5.3 

4.8 

Fully  irrigated . 

7.4 

6.0 

5.1 

48  Root  Behavior  and  Crop  Yield  Under  Irrigation. 

EXPERIMENTS  WITH  ALFALFA. 

The  alfalfa,  which  was  now  a  year  old,  was  examined  in  the  dry  land 
on  July  10  and  that  in  the  watered  area  2  days  later.  The  latter  had  been 
irrigated  for  the  first  time  on  July  2,  but  owing  to  the  greater  rainfall  the 
soil  was  quite  moist.  A  sufficient  supply  to  permit  root  growth  also  occurred 
in  the  dry  land,  even  to  a  depth  of  9  feet  (cf.  table  15),  although  at  the 
time  of  root  excavation  these  deeper  soils  were  very  dry.  Underlying  the 
surface  1.5  feet  of  dark  sandy  loam  in  the  dry  land  occurred  a  light-colored 
compact  sandy  clay.  This  gave  way  at  6  feet  in  depth  to  a  very  sandy 
soil,  while  between  7.5  and  9  feet  there  occurred  a  stratum  of  coarse  rounded 
stones  intermixed  with  gravel  and  sand.  The  roots,  which  in  September  of 
the  preceding  year  had  reached  a  maximum  depth  of  only  5.5  feet,  had 
made  a  marked  growth  and  extended  to  the  9-foot  level.  The  tap-root 
still  maintained  its  habit  of  growing  in  a  very  tortuous  course;  it  was  well 
supplied  with  both  large  and  small  branches,  the  latter  extending  to  near 
the  tip. 


Table  15. — Holard  of  alfalfa  plats  in  excess  of  hygroscopic  coefficients ,  1923. 


Date,  etc. 

0  to  0.5 
foot. 

0.5  to  1 
foot. 

1  to  2 
feet. 

2  to  3 
feet. 

3  to  4 
feet. 

4  to  5 
feet. 

5  to  6 
feet. 

6  to  7 
feet. 

7  to  8 
feet. 

8  to  9 
feet. 

9to  10 
feet. 

Dry  land: 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

May  24 . 

4.8 

2.5 

3.0 

2.4 

2.2 

July  11 . 

-2.2 

0.8 

1.8 

1.8 

0.7 

0.6 

1.3 

2.5 

1.0 

0.7 

Hygro.  coef . 

4.2 

4.4 

5.4 

5.3 

5.6 

5.9 

4.8 

4.6 

4.8 

4.9 

Fully  irrigated: 

May  24 . 

6.4 

3.2 

6.5 

8.2 

9.6 

July  2 . 

1.7 

1.9 

7.7 

7.9 

2 . 

(16.5) 

(16.5) 

(5.2) 

(6.0) 

11 . 

8.6 

12.7 

17.9 

12.6 

3.7 

0.9 

3.9 

6.4 

13.4 

16.1 

20.6 

Hygro.  coef . 

2.9 

3.1 

3.0 

5.0 

4.1 

2.7 

% 

1.4 

2.0 

2.3 

2  ;  1 

1.9 

Plants  in  the  irrigated  plats  had  made  a  no  less  marked  growth,  the 
tap-root  having  deepened  from  6  feet  to  nearly  10.  The  maximum  depth 
(9.8  feet)  would  probably  have  been  even  greater,  except  for  water  which 
had  seeped  in  and  not  only  wetted  the  soil  above  but  excluded  the  air  at 
this  depth  (cf.  Cannon,  1921).  As  in  dry  land,  branches  1  to  8  inches  long 
occurred,  but  these,  like  the  larger  branches,  ran  off  much  more  horizontally. 
They  were  rebranched  to  the  second  order  only,  while  many  in  the  dry 
soil  were  still  further  rebranched.  Also,  the  branches  and  tubercles  were 
fewer  in  the  deeper  layers  of  soil  than  in  the  dry  land.  Both  were  especially 
abundant  in  the  fifth  foot,  where  considerable  gravel  occurred  (fig.  7b). 
A  comparison  of  figures  7a  and  7b  shows  clearly  the  differences  in  the 
appearance  of  the  root  systems  in  the  two  fields. 

The  yield  of  a  second  cutting  for  1923  made  in  the  irrigated  plat  on 
July  21,  when  the  plants  were  26  inches  high,  was  1.6  tons  per  acre,  as 
compared  with  0.28  ton  from  the  second  cutting  made  on  June  26  in  the 
dry  land  when  the  plants  were  6  inches  tall  and  well  in  bloom. 


49 


Experiments  With  Wheat. 

EXPERIMENTS  WITH  WHEAT. 

Wheat  was  first  examined  on  May  24,  when  the  plants  in  both  areas 
were  about  6  inches  tall,  and  had  4  or  5  leaves  and  about  3  tillers  each. 
Practically  no  differences  were  found  in  the  root  habits  of  the  plants  in 
the  three  plats.  All  had  a  working  depth  of  about  18  inches  and  a  maximum 
penetration  of  2  feet.  Thus,  it  seems  clear  that  the  shallower  root  habit 
but  longer  branches  of  the  plants  of  similar  age  in  the  dry  land  the  previous 
season  was  a  direct  response  to  a  low  chresard  and  the  lack  of  a  supply  in 
the  second  foot. 

A  second  examination  was  made  on  June  16-18,  when  the  crop  in  the 
several  plats  averaged  nearly  2  feet  high,  that  in  the  fully  irrigated  field 
being  slightly  the  tallest.  In  all  fields  some  heads  were  beginning  to 
appear.  Just  as  the  crop  in  the  dry  land  was  11  inches  taller  than  the 
one  of  similar  age  in  1922,  so  too,  the  roots  occupied  a  much  greater  area. 
Although  the  lateral  spread  of  10  to  12  inches  and  the  number  of  branchlets 
were  about  the  same  in  the  furrow  slice  as  during  the  preceding  year,  10 
to  20  horizontal  roots  per  plant  now  occupied  this  area  as  compared  with 
only  6  or  8  during  the  drier  year.  As  pointed  out  elsewhere,  many  of  these 
roots  started,  but  dried  out  and  failed  to  develop  in  1922.  The  crop  was 
also  more  heavily  tillered  in  1923.  Moreover,  both  the  working  depth  and 
maximum  depth  of  penetration  were  about  10  inches  greater,  owing  to 
a  deeper  available  water-supply  (table  16).  Branches  were  even  better 
developed  than  in  1922  below  the  furrow  slice,  the  case  being  clearly  one 
of  a  fair  top  growth  under  conditions  which  now  demanded  an  increasing 
water  and  nutrient  supply.  Thus,  the  root  habit  more  nearly  approached 
that  in  the  irrigated  plats.  However,  in  the  latter,  shoot  growth  was  more 
luxuriant  and  the  roots  still  deeper.  The  working  and  maximum  depths 
in  the  lightly  and  fully  watered  plats  were  respectively  35  and  40,  and  48 
and  54  inches.  These  levels  were  very  similar  to  those  of  the  preceding 
year.  However,  a  direct  comparison  of  the  fully  watered  wheat  with 
that  of  1922  can  not  well  be  made  because  of  differences  in  soil.  While 
that  in  1922  was  grown  in  rather  pure  sand,  the  plat  in  1923  had  a  clayey 
subsoil  at  2  to  3.3  feet,  above  and  below  which  the  soil  was  very  sandy. 
The  form  of  the  root  was  like  that  of  the  lightly  watered  wheat  of  the 
previous  year.  The  latter,  during  1922,  was  perhaps  slightly  more  branched, 
especially  in  the  furrow  slice,  than  the  fully  irrigated  crop  which  had  been 
watered  on  June  8. 

A  final  examination  was  made  on  July  13-14,  when  the  grain  was  in 
the  dough  stage  of  ripening.  The  crop  in  the  dry  land,  which  had  been 
scarcely  damaged  by  the  hail,  was  3  feet  tall,  but  that  of  the  first  growth 
in  the  irrigated  plats  only  about  32  inches.  Here  a  second  growth  of  tillers, 
with  heads  only  2  inches  long,  reached  a  height  of  20  inches  (plate  6). 

In  June,  4.6  inches  of  precipitation  fell,  and  even  the  deeper  soils  of  the 
plats  previously  summer-fallowed  had  some  available  moisture  (table  16). 
The  root  habit  of  the  wheat  was  more  nearly  like  that  of  the  irrigated  soil 
than  of  the  dry  land  of  the  previous  year  (fig.  9d).  It  had  a  working  depth 
(3  feet)  fully  a  foot  deeper  than  that  of  the  previous  year,  while  the 
maximum  depth  of  55  inches  was  likewise  18  inches  greater.  The  yield 


50 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


was  in  accordance  with  the  fine  root  development,  being  at  the  rate  of  25 
bushels  of  grain  and  2.4  tons  total  dry  matter  per  acre.  In  the  lightly 
watered  soil  (irrigated  June  23)  the  plants  reached  a  working  depth  of  40 
inches  and  a  maximum  of  54  inches,  which  was  almost  identical  with  that 
in  the  fully  watered  plat  which  had  been  irrigated  on  three  different  dates 


Table  16. — Holard  of  wheat  plats  in  excess  of  hygroscopic  coefficients,  1923. 


Date,  etc. 

0  to  0.5 
foot. 

0.5  to  1 
foot. 

1  to  2 
feet. 

2  to  3 
feet. 

3  to  4 
feet. 

Dry  land: 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

Apr.  11 . 

10.5 

8.2 

8.5 

5.0 

1.0 

23 . 

9.8 

7.6 

7.8 

4.1 

-0.2 

30 . 

8.8 

5.6 

13.1 

12.1 

6.7 

May  24 . 

5.5 

3.7 

9.0 

8.6 

9.0 

June  8 . 

4.7 

1.5 

7.1 

6.1 

7.4 

June  16 . 

9.8 

5.3 

5.1 

3.8 

2.2 

July  17 . 

4.2 

0.0 

2.5 

2.3 

4.1 

Hygro.  coef . 

4.2 

5.4 

4.4 

4.3 

5.6 

Lightly  irrigated: 

Apr.  11 . 

11.7 

17.1 

19.3 

21.0 

18.2 

23 . 

9.6 

9.5 

10.7 

9.0 

7.1 

30 . 

6.5 

7.1 

10.4 

10.1 

9.2 

May  24 . 

3.6 

4.4 

5.3 

10.7 

8.4 

June  8 . 

4.2 

1.4 

1.9 

4.6 

11.3 

16 . 

8.0 

8.9 

14.8 

15.3 

10.3 

23 . 

5.6 

5.4 

9.7 

11.0 

23 . 

(16.6) 

(16.6) 

(9.5) 

(3.4) 

July  17 . 

2.9 

2.8 

8.9 

10.3 

7.1 

17 . 

(20.0) 

(20.0) 

(10.5) 

(3.4) 

Hygro.  coef . 

2.9 

3.1 

3.0 

5.0 

4.1 

Fully  irrigated: 

Apr.  11 . 

11.7 

17.1 

19.3 

21.0 

18.2 

23 . 

9.8 

9.7 

10.9 

9.2 

7.3 

30 . 

6.7 

7.4 

10.6 

10.3 

9.5 

May  24 . 

3.8 

4.9 

5.4 

10.8 

8.7 

June  8 . 

4.4 

1.7 

2.1 

4.9 

11.0 

8 . 

(13.1) 

(13.1) 

(14.2) 

(10.8) 

(4.1) 

16 . 

7.3 

7.9 

8.1 

13.6 

12.7 

23 . 

4.6 

4.4 

6.9 

13.8 

23 . 

(12.7) 

(12.7) 

(8.8) 

(2.0) 

July  5 . 

1.9 

1.7 

11.5 

13.6 

6 . 

(15.9) 

(15.9) 

(0.4) 

(0.2) 

17 . 

2.7 

3.5 

9.6 

14.4 

10.7 

17 . 

(14.4) 

(14.4) 

(7.6) 

(3.4) 

Hygro.  coef . 

2.9 

3.1 

3.0 

5.0 

4.1 

(table  16)).  Both  crops  had  fewer  branches  below  the  2-foot  level  than  in 
the  dry  land,  while  the  lightly  irrigated  one  had  a  few  more  and  slightly 
longer  rootlets  than  the  one  fully  irrigated.  For  these  crops  no  yield  was 
determined  because  of  the  damage  by  hail. 

In  order  to  still  further  check  the  effects  of  differences  of  water-content 
on  root  development  and  crop  growth,  wheat  was  grown  in  the  same  soil, 
but  under  different  degrees  of  moisture.  Four  oak  barrels  20  inches  in 
minimum  diameter  and  32  inches  deep  were  filled  with  soil  in  the  dry 
land,  care  being  taken  to  place  the  soil  in  such  a  manner  that  after  being 
tamped  in  place  it  occupied  the  same  relative  position  as  regards  depth 
that  it  had  previously  occupied  in  the  field.  These  were  filled  on  April  14 


Experiments  With  Wheat. 


51 


and  a  week  later  planted  with  wheat  at  the  rate  of  20  plants  per  container. 
Two  of  these  were  supplied  with  larger  amounts  of  water  than  the  others, 
as  is  indicated  in  table  17,  wooden  roofs  with  an  opening  an  inch  wide  to 
permit  the  growth  of  the  plants  being  used  to  exclude  nearly  all  of  the 
rainfall. 


Table  17. — Holard  in  excess  of  hygroscopic  coefficients  in  containers  with  wheat. 


Container. 

Average  water- 

Water  added  (gallons). 

Average  water- 
content  in  ex¬ 
cess  of  hygro. 
coeff. 

July  20. 

\JUJLLLCMAL  111 

of  hygro. 
May  1 

Depth, 

inches. 

coeff. 

4. 

Per 

cent. 

June 

1. 

June 

19. 

June 

26. 

July 

6. 

p.  ct. 

'  0  to  6 

3.2 

3.0 

2.2 

"N”r>9  1,2 

6  to  12 

3.0 

0.0 

12  to  24 

5.2 

2.7 

24  to  32 

2.4 

2.0 

0  to  6 

3.2 

2.5 

6.0 

8.0 

6.0 

1.8 

TsTna.  3,  4 

6  to  12 

3.0 

1.3 

)  12  to  24 

5.2 

4.0 

k  24  to  32 

2.4 

7.0 

At  the  time  of  harvest  the  plants  in  the  drier  and  wetter  soils  respectively 
were  17  and  23  inches  in  height.  The  former  had  about  2  and  the  latter  4 
tillers  each.  Differences  in  root  development  were  very  marked,  especially 
in  the  lower  layers  of  soil.  In  the  wetter  soil  the  roots  filled  the  soil 
to  the  bottom,  being  rather  evenly  distributed  throughout.  In  the  drier 
soil  below  2  feet  only  an  occasional  root  was  found;  however,  the  soil  was 
thoroughly  occupied  to  22  inches  depth.  Below  18  Inches  the  roots  in 
the  drier  soil  were  of  greater  diameter,  the  branches  were  nearly  twice  as 
numerous,  and  they  were  of  greater  average  length.  These  data  agree 
perfectly  with  those  just  given  for  field  development. 


52  Root  Behavior  and  Crop  Yield  Under  Irrigation. 

EXPERIMENTS  WITH  SUGAR  BEETS. 

The  first  examination  of  beets  was  made  on  June  8,  when  the  plants  were 
nearly  2  months  old,  3  to  5  inches  tall,  and  possessed  of  8  to  10  leaves  each. 
The  root  habit  in  the  three  plats  was  almost  identical,  the  branches  in  the 
dry  land  being  slightly  longer  (fig.  13).  An  examination  of  tables  14  and  18 
shows  that  both  nitrate  and  water-content  in  the  zone  of  root-growth  were 
very  similar  in  all  the  plats.  The  crop,  although  slightly  younger  than  that 
of  1922  when  first  examined,  showed  a  more  advanced  development,  prob¬ 
ably  because  it  had  been  planted  10  days  later  in  the  season.  It  may  be 
recalled  that  the  previous  crop  had  rapidly  developed  the  two  rows  of 
surface  roots  in  response  to  irrigation  and  belated  rainfall  respectively,  but 
in  1923  the  soil  was  sufficiently  moist  (table  18)  to  promote  a  good  early 
growth.  The  deeper  penetration  in  the  dry  land  than  during  the  preceding 
year  (maximum  over  19  inches),  as  well  as  the  widespread  horizontal 
branching,  may  also  be  attributed  to  a  better  water-supply  in  the  surface 
2  feet  of  soil. 

On  July  10-13  the  plants  had  15  or  16  rather  fully  expanded  leaves,  10  to 
12  inches  long,  and  a  top  diameter  of  15  to  16  inches,  those  in  the  dry  land 
being  the  least  developed  in  every  way  above  ground.  Larger  roots  than  in 
1922  occurred  in  the  surface  soil  in  all  the  plats,  probably  as  a  response  to 
the  rather  constantly  greater  water-supply,  especially  earlier  in  the  season 
(cf.  tables  10  and  18) ;  on  the  other  hand,  depth  of  penetration  was  also  less 
(cf.  figs.  11  and  14) .  In  the  dry  land,  usually  below  6  inches  depth,  strong 
laterals  arose  and  ran  off  nearly  parallel  with  the  soil  surface,  some  for  a 
distance  of  nearly  4  feet,  and  nearly  all  ended  in  the  surface  foot.  The 
profuse  branches  absorbed  much  of  the  precipitation,  which  was  2.1  inches 
during  May  and  4.6  inches  in  June.  The  shallowest  roots  had  not  yet 
reached  full  development,  being  mostly  short  and  unbranched.  The  char¬ 
acteristic  branching  in  the  second  foot  of  soil  is  shown  in  figure  14,  the  maxi¬ 
mum  root  penetration  seldom  exceeding  25  inches,  as  compared  with  30  to 
46  inches  in  the  much  drier  soils  of  the  preceding  year. 

Root  habit  in  the  fully  irrigated  plats  also  differed  from  that  of  the 
preceding  year,  being  shallower  and  spreading  more  widely  in  the  surface 
soil.  These  differences  are  probably  due  to  the  much  more  favorable  water- 
content  of  the  upper  soil  layers.  Many  horizontal  branches  were  excavated 
which  reached  outward  20  to  30  inches,  one  being  3.4  feet  long.  A  working 
depth  of  only  34  inches  was  determined  and  a  maximum  penetration  of  40 
inches  as  compared  with  54  in  1922.  The  greater  degree  of  branching  in  the 
more  compact  clay  soil  underlying  the  surface  16  inches  of  sandy  loam  is 
well  shown  in  figure  14b.  This  was  identical  with  the  1922  plat  and  also 
occurred  in  the  lightly  watered  area.  In  the  latter  plats,  which  had  not  yet 
been  irrigated,  the  tops  had  begun  to  wilt,  and  although  the  surface  soil 
was  better  occupied  with  more  and  longer  laterals  than  in  the  fully  irrigated 
plats,  root  depth  was  not  so  great.  A  working  depth  of  25  inches  (only  4 
inches  greater  than  that  in  the  dry  land)  and  a  maximum  penetration  of  3 
feet  were  determined.  In  both  cases  the  best  growth  occurred  in  the  moist 
surface  soils.  It  is  quite  possible  that  the  lower  soil  temperatures  had  some 
effect  upon  the  root  habit. 


Experiments  With  Sugar  Beets. 


53 


This  study  was  completed  on  August  20-21.  Growth  was  not  yet  com¬ 
plete,  as  was  indicated  by  the  presence  of  6  or  8  partly  grown  leaves  in 
addition  to  the  20  fully  expanded  ones  (24  in  fully  irrigated  soil).  These 
varied  in  length  in  order  of  increasing  water-content  through  12,  21,  and  24 
inches.  The  total  leaf  areas  of  typical  plants  selected  from  each  plat  were, 
in  order  of  increasing  soil  moisture,  7.26,  12.08,  and  20.46  square  feet.  The 
spread  of  tops  was  24  inches  in  the  fully  irrigated  plats  but  only  20  to  22  in 
the  others.  For  several  weeks  preceding,  the  tops  had  wilted  badly  in  the 
afternoons  in  the  dry  land  and  some  of  the  older  leaves  were  dying. 

In  the  dry  land  the  root  habit  was  similar  to  that  of  the  previous  excava¬ 
tion.  The  strong  tap-root,  now  2.3  inches  in  diameter,  usually  gave  off  4 
to  6  large  laterals  in  the  surface  10  inches  of  soil.  These  extended  later¬ 
ally  16  to  24  inches  or  more  and  then  turned  downward,  often  reaching  a 


Table  18. — Holard  of  beet  plats  in  excess  of  hygroscopic  coefficients,  1923. 


Date,  etc. 

0  to  0.5  foot. 

0.5  to  1  foot. 

1  to  2  feet. 

2  to  3  feet. 

3  to  4  feet. 

Dry  land: 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

Apr.  16 . 

3.9 

6.2 

6.0 

5.1 

6.7 

23 . 

9.8 

7.6 

7.8 

4.1 

6.3 

30 . 

8.8 

5.6 

13.1 

12.1 

6.7 

June  8 . 

9.2 

8.0 

8.4 

6.1 

1.0 

July  11 . 

0.0 

4.9 

6.3 

5.9 

1.1 

Aug.  21 . 

9.5 

3.5 

4.7 

3.6 

5.7 

Hygro.  coef . 

4.2 

5.4 

4.4 

4.3 

5.6 

Lightly  irrigated: 

Apr.  16 . 

5.2 

6.5 

13.2 

11.3 

2.3 

23 . 

9.6 

9.5 

10.7 

9.0 

7.1 

30 . 

6.5 

7.1 

10.4 

10.1 

9.2 

June  8 . 

9.1 

9.9 

13.5 

9.9 

7.9 

July  11 . 

5.0 

5.5 

12.3 

4.5 

7.4 

19 . 

2.7 

2.9 

9.8 

7.6 

19 . 

(14.6) 

(14.6) 

(8.2) 

(6.2) 

Aug.  21 . 

6.7 

7.0 

15.1 

10.9 

13.8 

Hygro.  coef . 

2.9 

3.1 

3.0 

5.0 

4.1 

Fully  irrigated: 

Apr.  16 . 

5.4 

6.9 

13.7 

11.8 

2.4 

23 . 

9.8 

9.9 

11.0 

9.7 

7.2 

30 . 

6.7 

7.5 

10.8 

10.7 

9.0 

June  8 . 

9.4 

10.2 

14.0 

10.3 

8.2 

July  2 . 

5.2 

5.6 

12.7 

10.0 

2 . 

(11.6) 

(11.6) 

(6.2) 

(3.9) 

11 . 

8.1 

8.4 

11.7 

11.6 

6.4 

19 . 

5.3 

5.8 

8.6 

10.1 

19 . 

(10.5) 

(10.5) 

(7.7) 

(3.8) 

Aug.  21 . 

8.0 

9.8 

14.5 

10.2 

13.6 

Hygro.  coef . 

2.9 

3.1 

3.0 

5.0 

4.1 

working  depth  of  56  inches.  This  downward-turning  tendency  was  very 
pronounced,  even  in  the  branches  originating  in  the  second  foot  of  soil,  and 
undoubtedly  resulted  from  the  drying-out  of  the  surface  layers  (table  18), 
tHe  branching,  often  to  the  fifth  order,  being  so  profuse  as  to  thoroughly 
occupy  the  surface  foot  with  a  dense  mass  of  rootlets.  Within  the  week  of 
the  examination,  however,  the  surface  8  inches  had  again  been  moistened 
and  a  mass  of  shiny  white  new  rootlets  1  to  7  inches  long  came  off  in  rows 
on  either  side  of  the  tap-root  to  the  very  soil  surface.  The  tap-root  with 


54 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


its  accompanying  network  of  branches  had  now  deepened  its  absorbing  area 
to  a  working  depth  of  56  inches  and  a  maximum  penetration  of  68  inches, 
the  soil  at  5  feet  depth  having  a  5  per  cent  chresard. 

The  root  habit  in  the  fully  watered  plat  was  practically  identical  with 
that  during  the  preceding  year,  except  for  one  outstanding  difference.  This 
consisted  of  the  wide  lateral  spread  of  the  roots  in  the  surface  foot,  a 
phenomenon  already  explained.  The  delay  in  the  development  of  the 
deeper  portion  of  the  root  system  recorded  at  the  last  examination  had  now 
been  fully  made  up.  In  fact,  the  even  more  luxuriant  tops,  with  the  leaves 
averaging  5  inches  longer  than  the  preceding  year,  made  such  heavy 
demands  during  the  hot  days  of  July  and  August  that  the  roots  had  some¬ 
what  exceeded  the  depth  of  the  last  season,  the  maximum  penetration  being 
80  inches  and  the  working  depth  72.  Seepage  water  now  filled  the  soil  at 
the  65-inch  level. 

Soil  strata  in  the  lightly  watered  plat  were  identical  with  those  described 
earlier  for  the  fully  irrigated  ones,  only  15  feet  away.  The  root  habit,  too, 
was  almost  identical  as  regards  surface  branching,  depth  of  penetration,  etc. 
In  fact,  it  seemed  that  the  single  irrigation  on  July  19,  together  with  the 
heavy  rains,  furnished  ample  moisture  for  normal  root-growth.  The  yield 
per  acre  of  the  dry-land  beets  was  6.7  tons,  while  those  in  the  lightly  and 
heavily  watered  plats  yielded  17.7  and  23.8  tons  respectively. 


Experiments  With  Potatoes. 


55 


EXPERIMENTS  WITH  POTATOES. 

Potatoes  in  the  dry  land  were  examined  on  July  6,  when  they  were  about 
7  weeks  old.  There  were  about  4  stalks  per  hill  and  the  plants  averaged  9 
inches  in  height.  The  general  character  of  the  root  system,  including  the 
wide  lateral  spread  (2.5  feet),  was  the  same  as  that  of  the  preceding  year. 
Working  depth  and  maximum  penetration  were  3  and  7  inches  greater 
respectively,  a  difference  probably  due  to  the  fact  that  the  plants  were  a 
week  older  and  growth  conditions  better  than  in  1922.  An  outstanding 
difference,  and  one  which  might  be  expected  in  the  moister  soil,  was  in  the 
length  of  the  branches.  Although  the  same  in  number  as  before,  they  now 
averaged  only  3  inches  long  (maximum  11  inches)  as  compared  with  5 
inches  (maximum  18  inches)  of  the  preceding  year.  Because  of  hail  injury, 
the  irrigated  crops  were  not  examined  at  this  time. 


Table  19. — Holard  of  potato  plats  in  excess  of  hygroscopic  coefficients ,  1928. 


Date,  etc. 

0  to  0.5  foot. 

0.5  to  1  foot. 

1  to  2  feet. 

2  to  3  feet. 

3  to  4  feet. 

Dry  land: 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

May  14 . 

7.2 

7.2 

6.9 

3.4 

3.3 

July  6 . 

0.4 

3.6 

7.7 

3.8 

7.2 

Hygro.  coef . 

4.2 

5.4 

4.4 

4.3 

5.6 

Lightly  irrigated: 

May  14 . 

11.6 

11.4 

17.5 

15.0 

5.1 

July  IQ . 

6.1 

6.8 

11.9 

11.1 

19 . 

(7.5) 

(7.5) 

(3.9) 

(0.8) 

Aug.  14 . 

8.3 

15.4 

18.6 

18.9 

14 . 

(5.5) 

(5 . 5) 

(3.0) 

(0.3) 

22 . 

10.1 

15.9 

18.0 

18.5 

22 . 

(5.3) 

(5.3) 

(3.2) 

'  (1.0) 

Hygro.  coef . 

4.6 

4.9 

8.0 

6.8 

4.0 

Fully  irrigated: 

May  14 . 

11.8 

11.7 

11.9 

15.5 

5.6 

.Tiilv  2 . 

7.1 

6.8 

12.2 

11.2 

2 . 

(6.2) 

‘(6.2) 

(1.7) 

(0.7) 

19  . 

6.8 

7.5 

10.1 

10.8 

19 . 

(8.9) 

(8.9) 

(3.0) 

(2.4) 

Ang.  14  . 

10.4 

13.2 

17.9 

18.6 

14  . 

(9.5) 

(9.5) 

(8.9) 

(2.6) 

22 

12.2 

13.5 

17.1 

18.7 

22  . 

(8.0) 

(8.0) 

(8.2) 

(2.1) 

Hygro.  coef . 

4.6 

4.9 

8.0 

6.8 

4.0 

These  studies  were  concluded  on  August  7-8,  when  the  11- weeks-old  crop 
was  in  full  bloom.  The  rainfall  for  July  was  less  than  an  inch,  but  a  heavy 
rain  fell  on  August  3.  The  lightly  watered  plats  had  been  irrigated  on 
July  19  and  the  fully  watered  ones  in  addition  on  July  2  (table  19).  The 
crop  in  the  dry  land  had  made  a  much  more  luxuriant  growth  than  during 
the  preceding  year,  the  17-inch  tops  lacking  only  a  foot  of  occupying  all  the 
space  between  the  3-foot  rows.  However,  the  plants  showed  plainly  the 
symptoms  of  drought,  many  leaves  having  died,  while  others  were  half  dry. 
Because  of  the  severe  hail  damage  (June  14),  plants  in  the  irrigated  plats 
were  much  smaller  than  formerly,  the  tops  not  exceeding  those  of  dry  land 
in  height,  although  spreading  more  widely  and  possessing  much  larger 
leaves. 


56 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


The  marked  differences  in  root  development  in  the  dry  land  during  the  two 
seasons  may  best  be  understood  by  a  comparison  of  figures  15a  and  15e. 
While  the  general  habit  in  the  surface  18  inches  is  the  same,  the  depth  to 
which  the  root  extended  after  turning  downward  is  remarkable.  In  1922, 
little  top  or  root  growth  occurred  after  July  1,  owing  to  lack  of  available 
water,  but  the  subsoil  the  next  season  was  sufficiently  moist  to  promote 
a  good  root  development  to  a  working-level  of  3  feet  (table  19),  a 
maximum  penetration  of  46  inches  being  attained.  Branching  was  profuse 
throughout.  The  previous  yield  of  19  bushels  per  acre  was  increased  to 
29.3,  the  tops  having  made  too  luxuriant  an  early  growth  to  resist  drought, 
which  later  caused  the  crop  to  dry  early  and  thus  reduce  the  yield. 

Root  habit  in  the  irrigated  plats  was  very  similar  to  that  of  the  preceding- 
year.  In  the  fully  watered  area  the  maximum  lateral  spread  (21  inches), 
working  depth  (17  inches),  and  maximum  penetration  (30  inches)  were 
very  nearly  as  before.  In  the  drier  soil  of  the  lightly  watered  plat,  the 
differences  in  root  habit  already  pointed  out  again  occurred,  viz,  longer 
surface  roots,  more  vertically  descending  ones,  more  profuse  branching,  and 
greater  working  and  maximum  depths.  However,  in  both  cases,  undoubtedly 
owing  to  the  damage  of  the  tops  by  the  hail,  fewer  main  roots  occurred.  In 
fact,  they  were  scarcely  more  than  half  as  numerous  as  before,  only  35  to  54 
occurring  on  a  single  plant.  The  yield  was  less  than  in  dry  land,  owing  to 
the  severe  hail  injury  to  the  irrigated  crops. 


57 


Experiments  With  Corn. 


EXPERIMENTS  WITH  CORN. 

The  corn  was  excavated  on  June  23,  when  the  crop  was  6  weeks  old  and 
about  a  foot  tall,  each  plant  having  7  or  8  leaves.  The  hail  of  June  14  had 
been  especially  severe  in  the  irrigated  plats.  Plants  in  the  dry  land  differed 
from  those  in  the  moister  irrigated  soil  (table  20)  chiefly  in  two  respects. 
The  widely  spreading  surface  roots  showed  a  more  marked  tendency  to  turn 
downward  near  their  ends,  some  reaching  depths  of  20  inches  or  more,  while 
those  in  the  irrigated  plats  had  mostly  just  started  to  turn  downward. 
While  in  the  moister  soil  a  few  vertically  descending  roots  from  the  base 
of  the  plant  had  begun  to  appear,  in  the  dry  land  these  were  quite  prominent, 
some  being  8  or  10  inches  long.  No  difference  was  found  in  the  two  irri¬ 
gated  plats;  in  fact,  the  water-content  was  about  the  same  in  both.  Con¬ 
trasted  with  the  preceding  year,  the  dry-land  plants  retained  more  of  the 


Table  20. — Holard  of  corn  plats  in  excess  of  hygroscopic  coefficients,  1928. 


Date,  etc. 

0  to  0.5  foot. 

0.5  to  1  foot. 

1  to  2  feet. 

2  to  3  feet. 

3  to  4  feet. 

Dry  land : 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

May  14 . 

7.2 

7.2 

6.9 

3.4 

3.3 

June  23 . 

5.1 

7.5 

5.1 

6.5 

9.4 

July  10 . 

0.0 

1.1 

4.3 

4.1 

7.5 

Aug.  17 . 

6.3 

1.8 

1.2 

0.9 

1.2 

Hygro.  coef . 

4.2 

5.4 

4.4 

4.3 

5.6 

Lightly  irrigated: 

May  14 . 

11.6 

11.4 

17.5 

15.0 

5.1 

June  23 . 

7.2 

6.8 

8.0 

10.9 

9.4 

.Tilly  5  . 

7.7 

7.5 

11.0 

10.0 

5 . 

(4.5) 

(4.5) 

(4.3) 

(1.7) 

10 . 

7.9 

7.3 

10.1 

,  13.4 

10.0 

Aug.  17 . 

10.1 

3.4 

4.6 

9.1 

11.6 

Hygro.  coef . 

2.9 

3.1 

3.0 

5.0 

4.1 

Fully  irrigated: 

May  14 . 

11.9 

11.8 

17.9 

15.5 

5.4 

June  23 . 

7.5 

6.9 

8.8 

11.0 

9.9 

July  5 . 

7.9 

7.8 

11.5 

10.6 

5 . 

(8.3) 

(8.3) 

(0.0) 

(0.0) 

10 . 

8.9 

6.6 

6.9 

10.2 

10.0 

21 

2  8 

2.9 

8.0 

11.1 

21 . 

(9.8) 

(9.8) 

(4.3) 

(2.3) 

Aug.  17 . 

7.6 

6.9 

7.5 

10.1 

14.9 

Hygro.  coef . 

2.9 

3.1 

3.0 

5.0 

4.1 

normal  root  habit,  i.  e.,  the  roots  spread  more  horizontally  in  the  surface 
soil,  and  the  branches  were  neither  so  numerous  nor  of  such  great  length. 
Likewise,  in  the  lightly  watered  plat,  the  roots  did  not  spread  so  widely  as 
in  the  drier  soil  of  the  preceding  year,  and  they  did  not  show  such  a  marked 
tendency  to  turn  downward  near  their  extremities  or  penetrate  so  deeply. 
Moreover,  the  development  of  the  vertically  descending  roots  was  not  so 
great. 

The  second  examination  of  corn  was  made  on  July  9-11.  The  average 
height  in  the  several  plats  in  order  of  decreasing  dryness  was  24,  33,  and  40 
inches.  In  all  fields  the  crop  had  made  an  excellent  growth  and  was  just 
beginning  to  tassel.  The  low  water-content  in  the  dry  land  (table  20)  was 
indicated  by  the  leaves,  which  for  a  few  days  only  had  begun  to  roll  during 


58 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


the  hottest  part  of  the  day.  In  the  dry  land  only  35  roots  per  plant  were 
found,  as  compared  with  33  to  45  the  previous  year.  Moreover,  the  working- 
level  was  3  inches  less  and  the  maximum  penetration  12  inches  short  of  that 
reached  in  the  drier  soil  of  the  preceding  season.  Otherwise  no  differences 
were  found.  In  the  fully  irrigated  plats,  where  the  clayey  subsoil  was  of  a 
much  lighter  type  than  in  1922,  the  roots  had  penetrated  to  a  maximum 
depth  of  46  inches  and  a  working  level  of  about  2.5  feet.  Aside  from  the 
greater  depth  (plants  of  1922  having  a  working  depth  of  only  2  feet),  little 
difference  was  noted.  As  before,  the  root  branches  were  fewer  and  shorter 
than  those  in  dry  land. 

This  study  was  concluded  on  August  17.  Owing  to  good  rains,  the  crop, 
even  in  the  dry  land,  had  made  a  luxuriant  growth,  the  height,  in  the  order 
of  increasing  water-content,  being  6.5,  7.3,  and  7.6  feet.  The  ears  were  well 
filled  and  the  kernels  beginning  to  dent.  On  August  18,  after  a  large  num¬ 
ber  of  measurements,  a  typical  plant  in  each  plat  was  selected  and  its  leaf 
area  (both  sides  of  leaves)  calculated.  This  was  found  to  be  6.86  square 
feet  in  the  dry  land  and  12.60  square  feet  in  the  lightly  irrigated  plat,  while 
the  plant  in  the  fully  watered  plat  had  an  area  of  12.88  square  feet.  As  for 
the  growth  of  tops,  the  root  system  in  the  dry  land  far  exceeded  in  extent 
that  of  the  previous  year.  Although  the  spread  was  about  the  same  (33 
inches),  the  working-level  had  been  lowered  from  30  (1922)  to  46  inches, 
and  similarly  the  maximum  penetration  from  46  to  66  inches,  the  soils  even 
at  this  depth  having  2  or  3  per  cent  available  moisture.  Moreover,  little 
difference  was  found  either  in  total  number  of  roots  or  number  or  length  of 
branches.  Root  development  in  the  fully  irrigated  plat  differed  scarcely  at 
all  from  that  of  plants  of  similar  age  in  1922.  They  had  the  same  wide 
lateral  spread,  and  while  the  working  depth  (46  inches)  was  6  inches  greater 
than  the  year  before,  the  maximum  penetration  (67  inches)  was  slightly 
less.  Seepage  water  was  found  at  this  level. 

Root  habit  in  the  lightly  watered  area  was  very  similar  to  that  in  the 
adjacent  fully  irrigated  plat.  At  all  depths  the  number  and  length  of 
branches  were  practically  identical.  Although  the  maximum  penetration 
was  slightly  greater,  the  working-level  was  about  5  inches  less,  a  difference 
due  perhaps  to  the  more  compact  clay  subsoil.  However,  as  in  1922,  the  first 
foot  of  soil  was  not  nearly  so  well  filled  with  roots  as  was  the  more  con¬ 
stantly  moist,  fully  irrigated  soil  (table  20).  Moreover,  the  main  roots  had  a 
more  marked  tendency  to  turn  downward.  Both  of  these  differences  were 
also  found  the  previous  year.  The  yield  in  the  dry  land  was  at  the  rate 
of  3  tons  of  dry  matter  and  51  bushels  of  grain  per  acre;  in  the  lightly 
watered  plat  it  was  5.8  tons  and  96  bushels  per  acre,  while  the  fully  irri¬ 
gated  plat  yielded  at  the  rate  of  6.7  tons  of  dry  matter  and  96  bushels  of 
grain  per  acre. 

Corn  was  also  grown  in  barrels,  the  soil  being  placed  as  in  the  case  of 
wheat,  and  two  of  the  four  containers  freely  supplied  with  water.  Two 
stalks  were  permitted  to  grow  in  each  container,  the  corn  having  been 
planted  on  May  12.  The  water-content  and  amount  of  water  added  are 
shown  in  table  21. 

At  the  time  of  examination,  the  plants  in  the  drier  soil  were  3.9  feet  tall ; 
the  dwarfed  leaves  had  been  almost  constantly  wilted  and  partially  rolled 


Experiments  With  Corn. 

Table  21. — Holard  in  excess  of  hygroscopic  coefficients  in  containers  with  corn. 


59 


Container. 

Average  water- 
content  in  ex¬ 
cess  of  hygro.  coef. 
May  14. 

Water  added  (gallons). 

Average  water- 
content  in  ex¬ 
cess  of  hygro. 
coef.  Aug.  17. 

Depth, 

Per 

June 

June 

June 

July 

July 

Aug. 

Per  cent. 

inches. 

cent. 

1 

19 

26 

6 

20 

1 

0  to  6 

3.2 

1 

0.5 

7  0 

Nos.  1,  2 . 

6  to  12 

3.0 

1.8 

<j 

12  to  24 

5.2 

4.1 

24  to  32 

2.4 

3  4 

0  to  6 

3.2 

1 

2 

2 

3.5 

2 

3.5 

6.7 

Nns.  3,  4 

6  to  12 

3.0 

6  2 

12  to  24 

5.2 

7  9 

24  to  32 

V 

2.4 

7.1 

for  many  days.  The  plants  in  the  wetter  soil  were  5.3  feet  tall,  were 
tasseling,  and  showed  no  signs  of  drought.  An  average  of  24  roots  was 
found  on  the  4  plants  in  the  dry  soil  and  the  same  number  in  the  moist. 
Roots  in  the  dry  soil  were  of  smaller  diameter,  more  woody,  and  tougher. 
Twice  as  many  roots  were  found  below  16  inches  in  the  wet  soil  as  in  the 
dry.  Although  repeated  counts  showed  that  the  average  number  of  root 
branches  per  inch  was  the  same  in  the  wet  soil  as  in  the  dry,  they  averaged 
fully  twice  as  long  (8  inches)  in  the  latter.  These  data,  in  general,  confirm 
those  found  under  similar  conditions  in  the  field. 


60  Root  Behavior  and  Crop  Yield  Under  Irrigation. 

SUMMARY  AND  CONCLUSIONS. 

During  the  seasons  of  1922-23  crops  of  alfalfa,  spring  wheat,  sugar  beets, 
potatoes,  and  corn  were  grown  at  Greeley,  Colorado,  in  soils  of  a  very 
similar  nature  as  regards  texture  and  chemical  composition,  but  varying 
widely  in  water-content.  The  growing-season  is  sufficiently  long  and  other 
conditions  are  favorable  for  plant  growth,  except  the  light,  unevenly  dis¬ 
tributed  rainfall  (12.7  inches  mean  annual),  which  makes  crop  production 
hazardous. 

Thirtieth-acre  plats  of  each  crop  were  grown  in  unirrigated,  lightly  irri¬ 
gated,  and  fully  irrigated  sandy-loam  soil.  Aside  from  these  differences, 
the  rainfall  during  the  second  year  of  the  experiments  was  so  unusually 
heavy  that  a  sharp  contrast  was  offered  in  the  holard  of  the  same  plats 
during  the  two  seasons.  This  was  still  further  checked  by  growing  crops  in 
large  containers  filled  with  similar  soil  but  of  different  water-content.  Con¬ 
tinuous  records  of  environmental  conditions  in  the  dry  and  watered  areas 
were  obtained.  During  1923,  air  and  soil  temperature,  humidity,  and  evap¬ 
oration  were  almost  identical,  but  during  the  drier  year  of  1922  above¬ 
ground  conditions  for  growth  were  a  little  more  severe  in  the  dry-land  plats. 
However,  making  due  allowances  for  the  small  differences  in  both  air  and 
soil,  other  than  water-content,  consistent  and  marked  differences  in  the 
development  of  the  root  systems  were  determined  as  the  crops  were  exam¬ 
ined  at  several  periods  during  their  growth.  Extensive  determinations  of 
water  relations  were  made  from  the  time  of  planting  until  the  maturity  of 
the  crops,  and  in  every  case  root  habit  was  found  to  be  very  responsive  to 
variations  of  this  factor.  In  general,  the  crops  with  the  most  extensive  root- 
systems  gave  the  greatest  yield. 

Turkestan  alfalfa  in  the  dry,  hard  land  differed  from  that  in  the  irrigated 
soil  by  pursuing  a  much  more  tortuous  course,  probably  owing  to  difficulty 
of  penetration,  by  having  longer  major  branches,  especially  abundant  in  the 
first  foot,  which  spread  less  widely  and  turned  downward  more  abruptly, 
and  in  the  earlier  development  of  the  plant  often  reached  depths  as  great 
as  those  of  the  tap-root.  Likewise,  secondary  and  tertiary  branches  were 
often  much  longer,  while  owing  to  the  slower  growth  of  the  tap-root  and 
largest  laterals,  branches  on  them  occurred  much  nearer  the  tip.  The  dry 
soil  had  a  very  retarding  effect  upon  the  growth  of  tubercles,  none  occurring 
at  the  end  of  the  season,  although  they  were  abundant  to  4  feet  in  irrigated 
soil. 

By  July  10  of  the  second  season,  which  was  very  wet,  the  dry-land  alfalfa 
had  extended  its  area  from  5.5  feet  depth  (where  dry  soil  had  occurred)  to 
9  feet.  In  the  watered  plats  growth  had  ceased  at  the  6-foot  level,  owing  to 
seepage  water  saturating  the  soil,  but  the  roots  now  extended  to  nearly  10 
feet.  The  yields  of  a  single  cutting  in  1922  of  0.12  and  0.52  ton  per  acre  had 
also  been  increased  in  proportion  to  root-growth  to  0.28  and  1.6  tons  in  1923. 

Marquis  spring  wheat  in  the  dry  land,  because  of  lack  of  moisture  in  the 
second  foot,  like  alfalfa,  spread  more  widely  in  the  surface  soil,  where  the 
moisture  was  replenished  by  the  heavier  summer  showers.  Here  many  of 
the  roots  died  of  drought  and  growth  was  greatly  retarded.  Those  which 
finally  turned  downward  first  spread  much  more  widely  than  in  the  plats 


Summary  and  Conclusions. 


61 


with  a  moist  subsoil.  Although  the  number  of  primary  branches  was  no 
greater  in  the  dry  land,  they  were  longer,  occurred  nearer  the  root  tips,  and 
tertiary  branches  were  much  more  numerous.  Dry-land  wheat  grew  but 
little  after  the  middle  of  June,  having  extended  its  roots  into  the  still  rather 
dry  second  foot  of  soil  to  a  working-level  of  only  2  feet,  as  contrasted  with 
3  feet  in  the  lightly  irrigated  plats  and  4.3  feet  in  the  more  loose  sandy  soil 
of  the  fully  irrigated  one.  The  height  of  crop  and  yield  in  the  progressively 
moister  soils  were  15,  41,  and  43  inches,  and  3,  32,  and  29  bushels  per  acre 
respectively,  the  sandier  soil  causing  a  decrease  in  the  yield  of  the  fully 
irrigated  plat/ 

In  1923,  when  the  soils  were  equally  moist,  the  first  examination  revealed 
no  differences  in  root  habit.  Later  the  area  occupied  by  the  root  system  of 
the  dry-land  crop  was  much  greater  than  in  1922,  owing  to  a  better  shoot 
development,  more  tillers,  and  a  subsoil  with  available  moisture  in  which 
none  of  the  roots  died.  The  lateral  spread  was  as  great  as  formerly  and 
the  working  depth  was  over  a  foot  deeper.  In  fact,  the  root  habit  was 
more  nearly  like  that  of  the  irrigated  soil  than  that  of  dry  land  of  the 
preceding  year.  The  crop  was  3  feet  high  and  the  yield  25  bushels  per 
acre.  Root  development  in  the  irrigated  soil  was  approximately  the  same 
as  the  preceding  year.  The  difference  in  root  habit  in  the  two  irrigated  plats, 
which  had  been  somewhat  emphasized  during  1922  because  of  variations  in 
soil  structure,  consisted  chiefly  in  more  extensive  branching  in  the  drier  soil. 
Both  plats  were  damaged  by  hail  and  the  yield  was  not  determined. 

Klein-wanzleben  sugar  beet  in  the  dry  land  had  its  normally  deeply  pene¬ 
trating  tap-roots  limited  because  of  dry  subsoil  in  its  early  development  to 
only  one-half  the  depth  in  moist  soil,  and  throughout  the  season  they  were 
1  to  1.5  feet  shorter.  Like  the  roots  of  other  dry-land  Crops,  they  pursued  a 
more  tortuous  course  and  were  branched  more  nearly  to  the  tip.  Branching 
was  more  profuse  and  sublaterals  more  abundant  than  in  fully  irrigated 
soil.  In  all  respects  the  lightly  watered  crop  was  intermediate.  By  mid¬ 
summer  the  dry-land  plants  had  neither  the  well-developed  shallow  portion 
of  the  root  system  nor  the  long,  deeply  penetrating  branches  (reaching 
depths  of  3  feet)  characteristic  of  those  growing  in  the  moist  soil.  They 
were  characterized  by  large  numbers  of  horizontally  spreading  major  laterals 
in  the  surface  at  4  to  18  inches  depth  where  available  water  had  been  con¬ 
stantly  most  abundant,  the  branches  becoming  shorter  with  increased  depth 
in  this  zone,  and  the  tap-root  with  its  profuse  short  branches  alone  pene¬ 
trating  to  the  3-foot  level.  Roots  in  the  lightly  irrigated  soil  were  again 
intermediate  in  having  the  shallow  surface  portion  of  the  system  poorly 
developed,  but  the  deeper  one,  which  was  quite  extensive,  had  its  major 
branches  much  more  widely  spread  than  in  the  wetter  fully  irrigated  soil. 
By  mid-September  the  dry-land  beets,  which  had  suffered  severely  from 
drought,  had  only  about  one-fourth  the  leaf  area  of  the  irrigated  plants,  and 
the  area  occupied  by  roots  was  also  much  less.  The  surface  roots,  stimu¬ 
lated  by  showers,  had  reached  a  lateral  spread  exceeding  that  in  moist  soil, 
while  abundant  deeper-seated  major  branches  had  penetrated  the  dry  sub¬ 
soil  2  or  3  feet.  As  in  alfalfa,  these  did  not  spread  widely  (seldom  over  7 
inches  as  compared  with  1.5  to  2  feet  in  moist  soil),  but  turned  down 
abruptly.  A  maximum  depth  of  4.5  feet  was  attained,  but  roots  in  moist 


02  Root  Behavior  and  Crop  Yield  Under  Irrigation. 

soil  extended  to  6  feet  deep.  The  lightly  watered  crop  had  a  lesser  root 
extent  in  the  surface  soil  than  that  in  dry  land,  but  greater  than  the  fully 
irrigated  crop.  It  was  also  intermediate  in  lateral  spread  of  deeper  branches, 
etc.,  as  compared  to  plants  in  moist  soil.  The  yield  was  2.5,  21,  and  22.5 
tons  per  acre,  increasing  progressively  with  water- content. 

During  the  much  more  humid  season  following,  the  beets  in  all  plats  were 
found  to  have  root  systems  practically  the  same,  and  were  thus  in  harmony 
with  the  uniformity  in  the  holard.  Later,  because  of  a  constantly  good 
water-supply,  the  surface  laterals  spread  much  more  widely  in  all  plats  than 
in  1922,  and  correlated  with  this  was  a  lesser  depth  of  penetration.  As  the 
surface  soil  in  the  unirrigated  plat  became  drier,  a  pronounced  tendency  was 
found  for  the  branches  to  turn  downward.  As  a  whole,  the  root  habit  more 
nearly  resembled  that  in  the  irrigated  plats  than  that  of  the  previous  dry¬ 
land  plants,  while  the  lightly  watered  soil  was  sufficiently  wet  so  that  little 
difference  was  found  between  the  root  habit  here  and  in  the  fully  watered 
plats,  both  resembling  that  of  the  fully  watered  plants  of  the  preceding 
season.  The  yield  per  acre  in  the  three  plats,  proceeding  from  the  driest 
to  the  fully  irrigated,  was  6.7,  17.7,  and  23.8  tons. 

Bliss’s  Triumph  potato  had  a  smaller  top  but  a  much  more  extensive 
root  system  in  the  dry  land  late  in  June.  Moreover,  the  branches  were 
much  more  abundant  and  longer.  Because  of  severe  drought,  little  further 
growth  occurred  either  above  or  below  ground  in  the  dry-land  potatoes, 
the  working  depth  being  about  2  feet.  The  fully  irrigated  crop  was  rooted 
mostly  in  the  surface  16  inches  of  soil,  where  the  laterals  spread  nearly  2 
feet  on  all  sides  of  the  plant.  The  lightly  watered  potatoes  had  an  even 
greater  lateral  spread,  more  roots  penetrated  nearly  vertically  downward, 
and  the  second  foot  of  soil  was  much  more  thoroughly  occupied.  Moreover, 
branching  was  much  more  profuse,  although  the  branches  were  no  longer. 
The  yield  varied  from  19  bushels  per  acre  in  dry  land  to  303  in  the  lightly 
irrigated  plat,  where  the  soil  was  more  sandy  and  production  greater  than 
in  the  fully  watered  one.  The  best  developed  root  system  was  correlated 
with  greatest  yield.  During  the  better  season  for  growth  in  1923,  the  dry¬ 
land  potatoes,  which  had  formerly  been  confined  to  the  surface  2  feet, 
penetrated  the  moister  subsoil  to  depths  of  nearly  4  feet,  while  the  yield 
was  increased  to  29.3  bushels  per  acre.  The  root  habit  in  the  fully  watered 
plats  was  about  the  same  as  the  preceding  year,  while  the  lightly  watered 
plants  showed  differences  similar  to  those  already  pointed  out  for  1922. 
The  yield  was  very  low  because  of  damage  due  to  hail. 

Corn  showed  marked  differences  in  root  habit,  even  when  only  6  weeks 
old.  Roots  in  dry  land  deviated  from  the  normal  shallow,  widely  spreading 
type,  and  more  grew  obliquely  or  directly  downward ;  those  in  intermediately 
dry  soil  spreading  and  then  turning  downward.  Number  and  length  of 
branches  increased  directly  in  proportion  to  scarcity  of  water-supply.  By 
midsummer  the  dry-land  corn  had  practically  completed  its  growth  both 
above  and  below  ground.  Drought  and  excessive  transpiration  had  stimu¬ 
lated  a  marked  root  growth.  The  widest  lateral  spread  of  shallow  roots 
(about  3.5  feet)  and  most  profuse  branching  now  occurred  here,  but  the 
working-level  (2.5  feet)  was  limited  by  dry  soil.  In  the  fully  watered 
plats  with  plants  a  foot  taller,  practically  the  entire  root  system  was 


Summary  and  Conclusions. 


63 


limited  to  the  surface  16  inches  of  soil.  Plants  in  the  lightly  irrigated  soil 
differed  in  less  thoroughly  occupying  the  drier  surface  4  inches,  in  a  lesser 
development-  of  new  roots  (also  due  to  dry  soil)  and  correlated  with  this, 
a  much  greater  extent  of  the  older  ones  to  a  working-level  of  33  inches 
(maximum  penetration  over  4  feet). 

The  mature  root  systems  in  dry  land,  like  the  tops,  showed  little  further 
growth  after  midsummer  and  the  yield  was  only  25  bushels  per  acre.  Those 
in  fully  watered  soil  had  extended  their  roots  well  into  the  fifth  and  sixth 
feet,  many  of  the  horizontal  laterals  having  also  turned  downward  and 
penetrated  deeply.  The  best  root  development  was  found  in  the  lightly 
watered  plats  with  somewhat  sandier  soil.  Although  the  fine  roots  in 
the  dry  surface  soil  were  fewer  and  the  lateral  spread  of  the  main  roots 
slightly  less,  the  depth  of  penetration  was  greater  (working-depth  about 
5  feet),  the  deeper  soils  being  more  thoroughly  occupied,  and  branching 
was  also  greater.  Here  again  the  highest  yield  (115  bushels  per  acre)  was 
correlated  with  the  best  developed  root  system,  the  fully  irrigated  plat 
yielding  102  bushels  per  acre. 

In  the  moist  soil  of  the  unirrigated  plats  in  1923,  the  young  roots  showed 
a  more  normal  surface  spread  with  less  tendency  to  turn  downward,  and 
the  branches  were  also  shorter  than  in  the  preceding  year.  The  top  growth 
was  far  more  luxuriant  aiTd  the  roots  made  a  much  better  growth.  They 
had  no  greater  lateral  spread,  but  the  working-level  (46  inches)  was  16 
inches  deeper,  and  the  length  of  branches  was  again  greater  than  in  the 
irrigated  plats.  Fully  watered  plants  developed  as  in  1922,  and  the  lightly 
watered  ones  were  not  so  different  from  them  as  during  the  preceding  year. 
However,  as  before,  in  the  latter  case  the  first  foot  of  soil  was  not  nearly 
so  well  filled  with  roots,  while  the  main  roots  had  a  more  marked  tendency 
to  turn  downwards.  The  dry  land  yielded  at  the  rate  of  51  bushels  of  grain 
per  acre  and  the  irrigated  plats  96.  / 

From  the  preceding  account  it  is  clear  that  the  roots  of  the  crops  employed 
responded  readily  to  the  changed  environment,  consisting  chiefly  of  differ¬ 
ences  in  chresard  and  air-content,  and  that  there  is  a  striking  correlation 
between  the  growth  of  underground  and  aerial  plant  parts.  Although 
the  root  habits  of  a  few  species  seem  to  be  controlled  largely  by  heredity 
and  show  little  plasticity  under  changed  conditions,  the  behavior  in  most 
species  depends  upon  the  operation  of  such  factors  as  water-content, 
aeration,  and  nutrients. 

Of  10  native  grasses  and  other  herbs  studied  by  Weaver  (1919)  in  two  or 
more  widely  separated  habitats,  7  showed  very  striking  changes  in  their  root 
habits  as  to  depth  of  penetration,  position  and  number  of  branches;  1 
exhibited  only  moderate  differences,  while  2  showed  practically  no  change. 
Pulling  (1918)  reported  that  several  shallow-rooted  forest  trees  as  well 
as  certain  deeply  rooted  ones  do  not  adapt  themselves  to  changed  soil 
conditions,  but  that  others  belonging  to  each  class  show  considerable 
plasticity,  and  Haasis  (1921)  likewise  found  great  variation  in  the  roots 
of  yellow  pine.  The  great  variability  in  the  rooting  habits  of  fruit  trees 
and  the  significance  of  this  in  orchard  practice  is  well  summarized  by 
Gardner,  Bradford,  and  Hooker  (1922  :  54,  586).  The  wide  adaptation 
of  black  walnut  to  so  many  soils  that  it  is  almost  universally  used  as  stock 


64 


Root  Behavior  and  Crop  Yield  Under  Irrigation. 


for  the  English  walnut  in  California  is  well  known.  Other  fruit  trees 
show  much  less  adaptation,  certain  varieties  failing  unless  grafted  onto 
other  stock  the  roots  of  which  adapt  themselves  to  soils  underlaid  with 
alkali  (Kelley  and  Thomas,  1920)  or  containing  excessive  moisture  (Sahut, 
1885),  or  to  very  exposed  or  dry  situations  (Sorauer,  1920).  Further  exten¬ 
sive  studies  by  Weaver  (1920)  have  shown  that  not  only  do  practically 
all  of  the  native  species  studied  vary  widely  in  root  habit,  but  also  many 
field  crops.  A  continuation  of  these  studies  with  field  crops  showed  that 
this  variation  was  sometimes  so  great  and  the  root  habit  so  profoundly 
changed  that  the  roots  were  scarcely  recognizable  as  belonging  to  the  same 
species  (Weaver  et  ah,  1922  :  69).  Crops  grown  in  soil  of  high  fertility 
have  roots  that  are  shorter,  more  branched,  and  more  compact  than  those 
in  similar  but  less  fertile  soil,  as  has  recently  been  confirmed  by  Crist  and 
Weaver  (1924).  Marked  contrasts  in  the  degree  of  ramification  of  roots 
as  they  penetrate  different  soil  strata  may  be  attributed  in  part  to  differ¬ 
ences  in  soil  fertility  (Bowman,  1911  :  66).  The  importance  of  proper 
soil  aeration  as  affecting  root  development  and  crop  yield  can  scarcely 
be  over-emphasized  (Clements,  1921).  “In  this  direction  [i.  e.  soil  aeration 
by  drainage]  we  have  possibilities  of  improvement  in  wheat  production 
[in  India]  which  will  settle  the  food  supply  of  the  world  for  generations 
to  come”  (Howard,  1916  :  19). 

/Thus,  root  distribution  and  the  functioning  of  the  part  of  the  plant 
above  ground,  in  so  far  as  it  is  conditioned  by  the  work  of  the  roots,  is 
under  control  to  the  extent  that  water-content,  soil-air,  nutrients,  and 
soil-texture  can  be  varied.  Marked  changes  of  root  habit  may  thus  be 
brought  about  by  methods  of  tillage,  use  of  fertilizers,  crop  rotations,  cover 
crops,  intercropping,  and  especially  by  irrigation  and  drainage. 

The  varying  needs  of  different  crops,  periods  when  each  is  most  sensitive 
to  applications  of  water,  the  best  method  of  applying  water  to  each  type 
of  soil,  and  its  effect  upon  the  soil  organisms,  as  well  as  the  best  rooting 
habit,  must  be  kept  constantly  in  mind.  With  respect  to  the  latter,  it 
should  be  clear  that  the  ideal  root  system  is  not  necessarily  the  one  with 
the  most  extensive  branching,  but  the  one  that  fully  occupies  the  soil  to 
a  sufficient  depth  and  within  a  sufficient  radius  to  secure  enough  water  and 
nutrients  at  all  times.  Where  the  water-supply  is  limited,  the  roots  must 
be  deep  and  not  held  near  the  surface  by  early  light  irrigation.  A  low 
holard,  within  certain  limits,  stimulates  greater  root  development,  and 
this  results  in  a  greatly  increased  absorbing  surface.  However,  this  advan¬ 
tage  may  be  overcome  by  the  competition  of  the  roots  of  too  many  plants 
grown  in  the  same  soil  area.  Notwithstanding  this  greater  absorbing- 
surface,  if  the  water-supply  is  restricted,  the  portion  of  the  plant  above 
ground  is  often  incapable  of  much  development,  as  was  strikingly  shown 
in  case  of  the  dry-land  potatoes  (p.  34).  Conversely,  it  is  usual  to  secure 
extensive  above-ground  development  from  a  limited  root  system  in  moist 
fertile  soil  (Weaver,  1919;  Haasis,  1921).  Unless  the  moisture-supply  is 
constant,  such  a  condition  is  dangerous  in  crop  production,  since  even 
moderate  drought  at  a  critical  period  may  enormously  lower  the  yield. 
When  the  absorbing  area  of  the  root  system  is  reduced  by  lack  of  aeration 
such  as  accompanies  the  rise  of  the  water-table,  the  plant  tries  to  adjust 


Summary  and  Conclusions. 


65 


itself  by  the  shedding  of  some  of  its  leaves  (and  fruits)  thus  reducing 
its  transpiring  area.  The  amount  of  shedding  is  often  directly  proportional 
to  the  degree  of  injury  to  the  root  system  (Howard,  1916  :  8;  Balls, 
1919  :  72).  Since  the  roots  are  killed  from  a  prolonged  lack  of  aeration, 
subsequent  lowering  of  the  water-table  due  to  drought  is  often  very  disas¬ 
trous  to  the  crop.  Under  conditions  of  unfavorable  water-supply,  not  only 
does  the  growth  of  the  plants  and  fruits  cease,  but  water  and  food  mate¬ 
rials  may  actually  be  withdrawn  from  the  storage  places  to  be  used  in  the 
vegetative  parts  (cf.  Coit  and  Hodgson,  1917). 

Finally,  it  should  be  kept  firmly  before  the  investigator  that  the  criterion 
of  yield  under  irrigation  should  not  be  the  maximum  production  per  acre, 
but  per  acre-inch  of  water  used.  Water,  not  land,  is  the  limiting  factor,  and 
we  will  learn  to  use  it  more  effectively  in  proportion  as  our  knowledge  of 
the  extent,  distribution,  and  activities  of  the  water-absorbing  organ,  the 
root  system,  is  increased. / 


BIBLIOGRAPHY. 

Balls,  W.  L.  1919.  The  cotton  plant  in  Egypt. 

Bowman,  I.  1911.  Forest  physiography. 

Cannon,  W.  A.  1919.  Modification  of  root  habits  by  experimental  means.  Carnegie 
Inst.  Wash.  Year  Book  No.  17,  pp.  83-85. 

- .  1921.  Root-growth  in  relation  to  a  deficiency  of  oxygen  or  an  excess  of  carbon 

dioxide  in  the  soil.  Carnegie  Inst.  Wash.  Year  Book  No.  20,  pp.  48-51. 
Clements,  F.  E.  1921.  Aeration  and  air-content.  The  role  of  oxygen  in  root  activity. 
Carnegie  Inst.  Wash.  Pub.  No.  315. 

Coit,  J.  E.,  and  R.  W.  Hodgson.  1917.  The  June  drop  of  Washington  navel  oranges. 
Cal.  Agr.  Exp.  Sta.  Bull.  No.  290. 

Crist,  J.  W.,  and  J.  E.  Weaver.  1924.  Absorption  of  nutrients  from  subsoil  in  relation 
to  crop  yield.  Bot.  Gaz.,  77,  pp.  121-148. 

Gardner,  V.  R.,  F.  C.  Bradford,  and  H.  D.  Hooker.  1922.  The  fundamentals  of  fruit 
production. 

Haasis,  F.  W.  1921.  Relations  between  soil  type  and  root  form  of  western  yellow 
pine  seedlings.  Ecology,  2,  pp.  292-303. 

Harlan,  H.  V.,  and  S.  Anthony.  1921.  Effect  of  time  of  irrigation  on  kernel  develop¬ 
ment  of  barley.  Jour.  Agr.  Res.,  21,  pp.  29-45. 

Harris,  F.  S.  1916.  The  irrigation  of  wheat.  Utah  Agr.  Exp.  Sta.  Bull.  No.  146,  pp.3-31. 

- .  1917.  The  irrigation  of  sugar  beets.  Utah  Agr.  Exp.  Sta.  Bull.  No.  156,  pp.  3-24. 

- .  1918.  Corn  under  irrigation.  Trans.  Utah  Acad.  Sci.,  1,  pp.  120-121. 

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No.  1026. 

Hole,  R.  S.  1918.  Recent  investigations  on  soil-aeration,  part  II,  with  special  refer¬ 
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Howard,  A.  1916.  Soil  aeration  in  agriculture.  Agr.  Res.  Inst.,  Pusa,  Bull.  No.  61. 

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agriculture.  Agr.  Jour.  India,  13,  pp.  416-429. 

-  and  G.  L.  C.  Howard.  1915.  Soil  ventilation.  Agr.  Res.  Inst.,  Pusa,  Bull.  No.  52. 

-  and  G.  L.  C.  Howard.  1919.  The  saving  of  irrigation  water  in  wheat  growing. 

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Jour.  India.  Special  Indian  Science  Congress  Number,  1919,  pp.  377—387. 

-  and  G.  L.  C.  Howard.  1920.  Some  aspects  of  the  indigo  industry  in  Bihar. 

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Knapp,  G.  S.  1922.  Relation  of  crop  yields  to  quantity  of  irrigation  water  in  south¬ 
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Pub.  No.  292. 

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crop  plants.  Carnegie  Inst.  Wash.  Pub.  No.  316. 

Widstoe,  J.  A.  1914.  The  principles  of  irrigation  practice. 


66 


JEAN  AND  WEAVER 


PLATE  1 


A.  — Yield  of  alfalfa  from  one  square  rod  of  dry  land  (left)  and  irrigated 

land  (right)  on  July  26,  of  first  season’s  growth. 

B.  — Yield  of  grain  from  one  square  rod  of  lightly  irrigated  wheat  (two 

containers  on  left),  fully  irrigated  but  more  sandy  soil  (center), 
and  dry  land  (right),  1922. 


•jrftVBBSlTY  OF  ILLIHWS  UBRAFa 


JEAN  AND  WEAVER 


PLATE  2 


Wheat,  1922:  A,  dry  land 


lightly  irrigated. 


"V 


ilffWSKTY  OF  ILLUWivLUSHAiit 


JEAN  AND  WEAVER 


PLATE  3 


Sugar  beets.  July  8,  1922 


A,  dry  land;  B,  fully  irrigated. 


■tWreBsrrr  of  humus  libbabv 


JEAN  AND  WEAVER 


PLATE  4 


Potatoes,  July  7,  1922:  A,  dry  land;  B,  lightly  irrigated;  C,  fully  irrigated. 


SlUTOSITY  OF  ILLINOIS  LIORAR) 


JEAN  AND  WEAVER 


PLATE  5 


Corn,  July  10,  1922:  A,  dry  land;  B,  lightly  irrigated. 


/WlY£B5irV  OF  ILUHUiJi  LI3Rftfi= 


JEAN  AND  WEAVER 


PLATE  6 


Marquis  spring  wheat  grown  on  fully  irrigated  soil  (left),  lightly  irrigated  but  less  sandy  soil 
(center),  and  dry  land  (right),  1922. 

Wheat  (3  feet  high)  grown  on  dry  land,  1923,  and  photographed  to  the  same  scale. 


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UNIVERSITY  OF  ILLINOIS-URBANA 

633J34R  C001 

ROOT  BEHAVIOR  AND  CROP  YIELD  UNDER  IRRIG 


3  0112 


020048143 


